C. Building Assemblies

David Whitfield’s 1994 document recommended that a handbook for the guidance of self-help housing be produced. This should, he said, “simply illustrate the necessary elements of house construction technology and highlight important issues and options available so that informed decisions can be made.”

Our charge for a government sponsored program is a little different than a self-help guide, but this document lays out the basic choices for different assemblies so that the Steering Committee can make informed choices.

The recent documents described in Section 1.B differ in how they recommend Nauruans should build. The differences are relatively small differences, and honest differences; the differences of people all trying to arrive at the right conclusions. There is no reason to expect complete agreement about how to build.

The purpose of this document is not to recommend still another way to build, but to look at the choices, to consider the thinking that goes into the choices, and to help frame trade-offs. The reason there are honest differences about how to build is because the trade-offs are complex and subtle, and subject to change over time.

The Steering Committee alone can give relative weight to these trade-offs. And the building program may even start out with one set of assemblies and then switch to another as they are priced or fabricated.

Disagreement within a narrow range seems likely. Experimentation within a narrow range seems entirely reasonable. Responding to changing circumstances, to changing prices, to the progress of the port, to the development of the skills of the trades, or to the performance of materials over time, seems inevitable.

The description of building assemblies that follows provides good examples of why it is difficult and even undesirable to have complete agreement on how to build. You should try different approaches.

1. Substrate, Footings and Ground Floor Slabs

a) Substrates

The substrate, the footings and the slabs will be considered together because the slope, drainage and bearing capacity of the substrate will affect the selection of a footing type, and sometimes the footing and the ground floor slab are poured separately and sometimes they are the same pour. It’s hard to consider these things separately.

The discussion of the substrate from remediated mines has been debated for a long time. Geoffrey Davey of the Nauru Lands Rehabilitation Committee wrote a report in 1966. He cites a 1954 study commissioned by the Australian government that confirmed the feasibility of knocking down the pinnacles and covering them with imported topsoil, but it cited the lack of water for growing anything. A study by the British Phosphate Commissioners in 1965 estimated a cost of $7300/acre, but over an enormous area of 3500 acres.

Housing is typically mentioned as one possible use for reclaimed land, but there are specific concerns for housing that would not apply to other uses. The NRC RONPHOS diagrams from 2021 show the pinnacles in a typical Nauru open pit phosphate mine. The secondary mining and remediation process requires that a very unbuildable landscape be made buildable. This is done by leveling the pinnacles and filling in the cavities. This kind of aggregate substrate should drain well and if properly prepared, it should have good bearing capacity. There will have to be soil borings done to test the capacity of the substrate before buildings are built.

The engineers undertaking the remediation are confident about providing a buildable pad for housing, but other than the Australian Detention facility, we are unaware of where there has been experience building over this kind of landscape, and we are unaware of any observation of similarly reclaimed areas over time, that might offer insight into settlement issues.

Typically an engineer will want a substrate consisting of fill brought in in shallow layers that are then individually compacted, one layer at a time and over a large open area. The fill from secondary mining process, by contrast, is in small isolated cavities that can’t be rolled and so the mechanics of this compaction are unclear, and we don’t know the size range of the aggregate.

The combined topping layers over the leveled pinnacles from secondary mining is 200 mm and so an additional consideration is differential settlement, which may be just as important as the compaction of the cavities. If fill is not properly compacted, or if there is insufficient fill over the pinnacles, the fill may settle where the pinnacles do not settle. This kind of condition could put stress on the footings that does not occur in conditions of minimal and reasonable settlement of continuous fill.

Because the remediation is being undertaken by one party in one time frame, and construction by another party in a different time frame, there may be an incentive to prepare a site in ways that do not ensure a decent substrate for a building’s foundation. Some consideration should be given in advance of remediation, to aligning everyone’s incentives or there will be a risk that site preparation costs will be minimized by those preparing the site and shifted to those constructing the houses. And the worst outcome would be differential settlement that was only noticeable over time. The structural integrity of the houses depends on the proper preparation of the substrate.

b) Footings and Ground Floor Slabs

SECTION 1.C

■ Secondary mining will occur in a couple of stages. The pinnacles will be knocked down and this will make secondary deposits accessible. The secondary removal will create pinnacles again, and the pinnacles will be cut down and used for filling the voids of the secondary removal. Then there will be several topping layers totaling 200 mm.

■ The text raises question about differential settlement and the effect on the selection of a foundation types. It also raises questions about the incentives of separate parties for mining and site prep. The depth of the topping is probably not sufficient to allay concerns about differential settlement. Engineers should be consulted, borings taken and bearing capacities determined. The crushed rock should drain well and have good bearing, but if differential settlement takes place it will be cause of the difficulty in compacting crushed rock fill in these small but deeper cavities.

■ To our knowledge there has only been one building built on a remediated phosphate mine - the Australian Detention Centre - and we don’t know if the settlement of the substrate has been observed over time. We would like to have any drawings of the facility and the foundations, that might be available.

(3) Raised Wood Floors

Regardless of the foundation type, you want consistent bearing capacity through the building sites. This provides maximum flexibility in choosing a foundation type. Figure 4 describes several basic types of foundations that will be reviewed here - a monolithic slab, a single pour that acts as both slab and footing; a continuous spread footing with a stem wall and a raised slab on compacted fill; a pier foundation, a crawl space with a wood floor, a raised slab formed in place, and a thick matt slab in the event substrate quality varies.

Whitfield recommended a slab on grade. The Smart House has a crawlspace with a wood floor in one part and a matt slab and a raised poured in place slab in another part. Both portions are on poured concrete piers. So you have a range of choices and have to evaluate the tradeoffs of each one.

The housing committee, for example, advised us that the labor costs of the pier foundations of the Smart House came in relatively high. This, of course makes ventilation relatively more expensive and slabs on grade or raised slabs relatively more affordable. With this information the committee is better prepared to consider the tradeoffs of cost and ventilation. As you get more information on the costs of any assembly, you will make more informed decisions.

The bearing capacity of the site has to be considered. The fall of the site has to be considered. Runoff has to be considered. Humidity and rot have to be considered. The cost of the rough carpentry to form the concrete has to be considered. Sourcing and shipping costs have to be considered. Studies always cite the fact that there are sources of aggregate on the island, but concrete requires clean fresh water, clean sand free of salt, steel, and cement, and some of these components will be imported at great cost.

(1) Slabs on Grade

Whitfield didn’t clarify whether the slab he preferred was on existing grade or raised up on compacted fill. The least expensive option is usually a relatively thin slab on grade, where the slab thickens at the edges to act as a footing as well. This type of foundation combines two concrete pours into one pour. It requires a flat site, and it requires a comprehensive site drain age plan that will keep water away from a slab very close to adjacent grades.

(2) Raised Slabs on Grade

If you don’t have a flat site or if runoff from upslope is a concern you may need to raise the floor. This can be done with piers, or with a continuous footing below several block courses. If you have a continuous footing and continuous stem wall you can fill inside it, compact the fill, and use the fill as formwork for a raised slab.

■ Diagram A describes the composite floor framing plan of the two room deep Smart House. The other diagrams are the same size but illustrated alternate floor assemblies. The Smart House has a front tier of rooms with a raised wood floor supported by piers, and over the water tanks. A perimeter beam catches joists between piers. The piers provide ventilation required of raised wood floors. The bedroom wing is over a raised poured in place slab on concrete piers at small intervals.

■ Diagram B s hows a wood floor system over the same entire area. Piers are more widely spaced and fewer in number. This requires slightly larger perimeter beams. A centre row of piers would support the wall between the living room and bedroom wings.

■ Diagram C shows the same area with perimeter stem walls, like those of diagram B in the foundation types. Stem wall systems require two pours. The walls are above a continuous footing. The foundation walls would be filled and the earth compacted and a raised floor slab poured over the compacted fill.

■ Diagram D shows a slab on grade - a single pour for the footings and the thin floor slab. This is the most economical floor type, but it requires flat sites and sites that drain away from the house.

Figure 4

■ This is a series of cross sections describing different foundations. The upper left foundation, A, is a single concrete pour that combines the thin floor slab and the footing. This is a very economical foundation, but it requires fairly flat sites. Diagram B requires two pours, a footing and a separate slab. Between these pours, masons build a stem wall, within which compacted fill provides earth formwork for the raised floor slab.

■ Diagram C is a matt, or raft slab. Matt slabs use a lot of concrete. The matt slab at the rear of the smart house is 0.6 meters thick. This type of foundation would typically be used where the bearing capacity of the substrate is inconsistent. See the description of remediated substrates.

■ Diagram D is a raised poured in place slab spanning a continuous block stem wall. It has the cost of two concrete pours, but the floor slab itself has the considerable cost of temporary wood formwork and reinforced steel. It does provide a less permeable barrier between the crawlspaces and the first floor and would not be prone to the rot of wood rafters in unventilated spaces.

■ Diagrams E and F both have wood floor joists over a crawlspace. E is built on block piers, and F is built on a continuous stem wall. Piers provide the ventilation required for wood framing, but they require a perimeter beam to catch joists between piers. Continuous stem walls require vent panels. Both assemblies would support wood walls above. Owing to the humidity of the climate and the prevalence of termites, a crawlspace could be lined by a thin floating slab on grade.

■ Diagram G describes the foundation under the bedroom wing of the Smart House. It is a composite foundation containing a matt slab, poured piers and a raised poured in place floor slab.

■ Without doing detailed take-offs, you can think of each option in terms of the amounts of labor and material, sometimes moving money from one to the other. Concrete is either formed by boards of ply wood, or earth. There are either one or two or even three pours in these options. Raised poured in place slabs are especially costly because of the formwork.

The main rooms of the Smart House have poured piers and wood floor joists elevated from grade. (There is a variant with a continuous concrete block stem wall) Piers require a beam parallel to the piers to pick up joists that fall between the pier spacing. Raised floors requires a crawlspace and good ventilation to prevent the rotting of the floor joists. It is difficult to inspect crawl spaces for deterioration. Crawlspaces have to be kept clear of vermin. Wood floor joists will be sourced off island, and so they come with transportation costs and require minimal rough carpentry skills. The housing committee has told us that the grading of lumber is unreliable.

Whitfield and Carstairs acknowledged the advantages of piers, crawlspaces and raised floors for cooling but in the end recommended slabs on grade for economy. The foundation labor costs of the Smart House, and the inability to rely on properly graded lumber for floor joists both argue for either slabs on grade or raised slabs.

(4) Raised Slabs Poured in Place

There are two common ways to have a raised slab - with prefabricated concrete plank, and formed and poured in place steel reinforced concrete. While plank is cheaper if it can be sourced nearby, it is unrealistic in Nauru because of shipping costs and the setup costs of a plant are prohibitive.

The bedroom wings of the Smart House have a grid of poured piers at tight intervals that sup port a raised poured in place slab. A raised poured in place slab is still expensive compared to other options but some material can be sourced on island and if you have people skilled in placing reinforced steel, it will provide another trade for Nauruans.

Wood formwork for spanning poured in place slabs is more expensive than formwork for walls or piers. Whereas a continuous stem wall foundation with a slab on compacted fill uses dirt for form work, a raised slab will be formed in place with temporary wood form work. Likely this is why the costs of the Smart House foundations are high. Poured in place slabs, for all their costs, provide raise floors without the maintenance concerns associated with wood floor systems over crawl spaces.

(5) Matt Foundations

A matt foundation, or raft foundation, is a thick continuous slab at or below grade. It is expensive because of the amount of concrete that is required but is usually used to address substrates that might have differential settlement, like a remediated mine. It appears that the Smart Houses uses a matt foundation under the stacked bedroom wing, but it uses concrete piers above the matte slab and then a raised poured in place slab.

If the substrate of the remediated mine sites is properly prepared matt slabs should not be necessary. However, if it proves difficult to avoid differential settlement of the substrate, they might be necessary. A structural engineer should be involved in this decision.

c) Conclusion

Whitfield recommended slabs on grades. The Smart House has two types of raised foundations. Raised foundation generally cost more for one reason or another. But if skills are to be developed slightly, more labor intensive foundation types might be acceptable.

And if slightly more labor intensive foundations allow for systems with materials that can be sourced on island then higher labor costs might be offset by reduced shipping costs. But with regard to concrete it is necessary to consider its components- aggregate, clean sand, clean water, cement, and steel.

The housing committee said that aggregate from ground up pinnacles can be used for concrete. They said sea sand used to be used in mixing concrete. This is not an acceptable source for concrete but the committee also said that the pinnacles of the mine can be pulverized for use as sand. The clay required for cement has to be imported and according to Whitfield, the costs of imported cement are quite high. Steel will be imported at great cost. The housing committee has built in the cost of these imported materials.

So while block and concrete is nominally sourced on island, some of its components will still be imported and so in considering matt slabs, especially, but also poured piers, tie beams, tie columns, rake beams, and filled block cells, care should be taken to monitor the volumes of concrete for various foundations.

If more durable systems cost more at the time of construction, a life cycle analysis might justify greater upfront costs. On the other hand, any increase in the cost of construction may reduce home ownership and make renting relatively more attractive.

Finally, in a competitive building market, there is a disincentive for any one builder to incur unnecessary up-front costs, even if more costly methods increase the life cycle of the house. This is the case in mature real estate markets in the United States. If durable methods of construction are to be encouraged there will have to be incentives to build houses that will be worth more after twenty or thirty years, rather than depreciated. This won’t happen naturally and in the markets where we work, this problem is unresolved. If this is a sustainable initiative, incentives have to be in place so that durability is encouraged and not naturally disincentivized as it is here in the States. Part of having this be a model project should be thinking about how durable systems and longer term horizons can be encouraged. If durable methods of construction can be incentivized, you will leap ahead of the U.S. housing market in some ways.

2. Walls

a) Envelope Efficiency

An inordinate amount of the construction budget is in the building envelope. Therefore, one of the best measures of efficiency and cost effectiveness of a house is envelope efficiency. Envelope efficiency is the ratio of the enclosing envelope to the enclosed area. It can be an area to area calculation. It can be a linear to area calculation. It needn’t be tracked obsessively, but it is a good idea to understand its broad implications.

The most efficient house is square. Envelopes become increasing inefficient as plans thin and elongate. Some modifications are more expensive than others. If you widen an elongated plan the cost increase will be less than directly proportional to the area added. If you lengthen an elongated plan the increase in cost will more nearly approach a proportional increase in costs.

For example, if you widen a 3.5 meter by 10 meter volume by half a meter you will increase the area by about 14% but you will only increase the linear feet of building envelope by one meter from 27 linear meters to 28 linear meters.

Flooring or roofing will increase roughly proportionally to the increase in floor area. Building shell trades will increase by much less. Roof framing will only increase marginally.

If there were no offsetting considerations, rational housing would converge on square plans. But elongated plans get more daylight and better cross ventilation. And they may be better at forming streets or courtyards. We work a lot with thinner plans. They are small luxuries, and we might be better off scrutinizing other forms of inefficiencies that don’t offer off setting improvements in the quality of habitation.

Whitfield recommended plans a single room deep if possible, which means he gave more weight to the benefits of better light and ventilation, and relatively less to the increased costs of a thin house. The Smart House is two rooms deep, which probably means that envelope efficiency was given slightly greater weight than cross ventilation. This is one of many examples of how people arrive at different conclusions about how to build on Nauru. But everyone makes these decisions in good faith.

b) Materials

It was a little surprising to see in the 2011 Census how common wood and even metal houses were. Whitfield cites surveys that reflect a Nauruan preference for masonry. The Steering Committee may have a preference for a particular wall material or may want to encourage a mix going forward. Preliminary feedback from the housing committee suggests a preference for concrete block walls.

■ Wall openings are the most expensive part of the building envelope, which is the most expensive assembly in a building. Whitfield recommended a percentage of openings of 50-80% because he placed a lot of weight on cross ventilation. The Smart House, on the upper left, has a much smaller percentage of openings because they placed relatively more weight on costs. Keeping costs down increases the accessibility of home ownership. The percentage of openings will vary from one exposure to the next.

■ It is almost impossible to hit the high end of Whitfield’s recommended range. 80% would be like an enclosed porch, and maybe this can be an additive option. The percentage of opening in the Smart House could be higher because the plan is two rooms wider and less conducive to cross ventilation that the single room plans Whitfield liked.

■ It mig ht be low for reasons of security but when we have real sites and configurations, secure exposures in courtyards might have better ventilation without compromising security. In the next phase we will probably start with about 30% openings and go a little either side of that, depending on the sun exposure and the street and block setting.

Wood and concrete block should both perform well against winds loads provided there is sheathing on wood frame walls, but plywood is expensive and is not used on roofs. Sourcing, labor skills, transportation costs, and climate will be bigger considerations in deciding between wood and block. If you can set up a block plant and a concrete batching plant on island it will eliminate sea transport costs. Reinforcing steel would still be shipped. Wood is lighter but would be shipped in. According to the housing committee, grading of lumber is unreliable.

Wood can be used in most climates, but wood species vary in rot resistance. New growth generally underperforms old growth woods. Old growth woods are increasingly rare. Wood is renewable and block and concrete and cement have high embodied energy. But Whitfield is clear on the danger posed by termites- both flying termites and nests in the ground.

Either material should have a vapor barrier on the outside. With block this is generally obtained with paint vapor barriers. Stucco over block is more forgiving of the masonry skills and it covers transitions between block and concrete It looks like it is uncommon on Nauru but the housing committee says it is the customary. It doesn’t appear to be used on the Smart House. The vapor barrier for wood framing is straightforward and light weight. There is cost in the siding over wood walls. The siding is painted and provides additional moisture barriers. Both stucco and siding require ongoing maintenance.

Wood walls are more readily insulated to higher R values, but the housing committee says that insulation is unusual. Block walls are generally insulated by furring the inside of the walls and is thinner with lower R values but again, the housing committee says that the interiors of block walls just have a stucco coat applied directly to the block

When all factors are considered, block walls appear to be the more likely choice.

c) Wall Openings

If construction costs lie inordinately in the building envelope, envelope costs lie inordinately in openings in the envelope. Whitfield recommended 50 to 80 percent opening in the walls for cross ventilation. This seems very high. A low percentage of openings would reduce costs considerably and reduce heat gain. But the cross ventilation and natural light provided by a high percentage of openings is very desirable.

The jalousie windows used on the Smart House, and apparently common on the island, are distinct and attractive. We would be interested to know more about the performance of the openers in a salt environment, and about their water tightness. Also it would be important to have a supplier with the ability to service and repair any windows you use. For a given area of glass, windows are generally much less expensive than doors. The housing committee says that shutters are a common alternative to windows.

SECTION 1.C

■ This sheet shows the range of roof forms considered at greater length in the text. There are three basic types with different gable end eave conditions. Each roof form has construction assembly implications, which will also be developed at a larger scale. Hip roofs are easier to frame with trusses but possible to stick frame. They have the advantage of having continuous horizontal eaves and horizontal tie beams at the tops of the walls. Nauru has some examples of hips transitioning into gables. This would accommodate a porch, as an example, as a lower space and the main rooms under the higher open gable; the exposed gable providing ventilation.

■ The three middle diagrams show gables, which seem to be the most common roof form on the island. The variants are distinguished by that material of the gable end wall the relationship of the gable wall to the roof. Parapeted gables don’t seem to be used on the island. Raking eaves, which are hard to build, typically protect the upper wall from driven rain. There is an entire sheet dedicated to gable end eave construction.

■ Shed roofs, single pitches, are common and typically extend past both the end walls and the high side walls, like on the Smart House. Care has to be taken to keep water on the high side soffit from running back to the walls.

The housing committee says that insect screens are rare but that mosquitos and other insects are common. In considering window types, consideration needs to be given to allowable percentage of opening. Jalousies can open 100%. Whitfield cited complaints about the siding windows of the 1990’s kit houses for not being able to open more than 50%.

Windows and doors in wood walls are a little more expensive to flash and waterproof. Windows and doors in masonry walls are most prone to leaks where the frame meets the rough framing, and less likely where the frame meets the sash.

d) Conclusion

The Smart House building sections show both block and wood framed walls, just as they show both wood and concrete floor systems. We assumed that block would have an edge over wood but that will vary with the ability to produce block and concrete on the island, on transportation costs, the skills of the trades, the premium placed on relatively clean, renewable resources, the availability of durable faming species, and the ravages of the climate and environment.

The use of wood is appealing because it is a renewable resource, but fast growth woods are less rot resistant. When you add the cost of siding and flashing any price advantages may disappear. Whitfield cites surveys which say that the majority of Nauruans prefer block over wood. This may derive from the perception of greater durability. Life cycle costs will tilt cost advantages to block, and better maintain the value of initial investments.

Based on what we have heard from the housing committee, the energy performance of walls and windows is rarely considered. Wood isn’t reliably graded. Plywood is prohibitively expensive. If block is made on island and is preferred by Nauruan homeowners, the arguments for wood aren’t very strong.

3. Roofs a) Roof Forms

Historical and current examples of Nauruan houses show gable roofs and shed roofs, and flat roofs, and hip roofs and hips going into gables. The Smart House has a lower shed leaning against an upper shed sloping in the opposite direction. This variety of basic roof forms is evidence that, even with the benefit of time, there is no right way to approach a basic building assembly.

■ Gable roofs, which are common on Nauru, have raking eaves on the gable ends. This is usually a complicated assembly and can be constructed in several ways. Diagram A shows a masonry parapet extending beyond the roof. The top of the wall would be flashed. There would be flashing where the roof meets the raking gable wall. This is not a common assembly on Nauru for two reasons. Masonry gable ends are not common, and the upper walls is not afforded shade or protection.

■ Diagrams A and B both show plywood roof sheathing, which is prohibitively expensive on Nauru. The plywood extends to a rafter bolted to the wall. The sheathing is edge nailed to this rafter providing continuity between the wall and roof assemblies.

■ Diagram B shows a masonry gable end, which eliminates wood there, but it requires forming a concrete rake beam at an angle. The eaves project to protect the upper wall. The rafters extend to the roof sheathing. A short ladder is formed over the rake beam, supporting the cantilevered eave.

■ Diagram C reflects framing more common to Nauru and reflected on the Smart House. The Smart House has shallower rafters and deeper purlins, and the purlins form the eaves. There is a deep raking fascia that is essentially hung from the extended purlins. There is no plywood roof sheathing. The gable end wall is framed with wood.

■ All gable roofs have raking eaves. Hip roofs do not. Diagram D shows a continuous horizontal eave that can be open or closed. It is shown closed here to protect the roof truss extensions. Hip roofs can be stick framed but are more commonly framed by trusses, and the lack of trusses on the island may make gables more common than hips.

■ The top row of diagrams show roof trusses, and diagrams D through H show different forms of framing with dimensional lumber. Diagrams vary in how the eaves are framed and how the outward thrust of the rafter is counteracted. Trusses all have bottom chords at the ceilings that counter thrust. Trusses require engineering and a modest plant and may not be an option on the island.

■ Diagram A shows the eaves formed by an extension of the top chords of the truss. The soffit framing member would be added in the field. These eaves are enclosed and protected from the elements. Diagram B also forms the eaves with an extension of the top chord, but the eaves are open and subject to the ravages of the environment. Diagram C address this by scabbing a separate rafter tail onto the trusses so that if an eave assembly need to be repaired, the structural members of the roof are separate and protected inside the wall.

■ Diagram D has open eaves formed by rafter tails scabbed onto the rafters. It has a collar ties at the ceiling. The width of the span would be limited by the length of this collar tie. The flat ceiling hides the scabbing of the rafter tails. The ridge is nonstructural because of the collar ties. Diagram E has a higher collar tie and the roof framing is open to the rooms below in order to let warm air rise. The ridge is non-structural. When framing is visible from below, it requires better workmanship.

■ Diagram F has no collar tie because the ridge is a structural ridge which renders the rafters a simple span with no outward thrust. Structural ridges have to post down at intervals and so this affects the flexibility of the plan.

■ Diagrams G and H show shed roofs which are common on Nauru and used on the Smart House. Shed roofs work best when their high end leans against a taller volume like in diagram G, as they do in the front room of the Smart House. When the upper end is open as it is on H, water is prone to flowing down the underside of the eaves back to the wall. The eaves are more prone to rot and the walls to leaking. The Smart House addresses this with a small return pitch.

There are some basic considerations for making a decision about the form of the roof. First, virtually all roofs slope because water must be diverted. Even what we describe as flat roofs slope behind a parapet wall and are either drained internally or through the parapet.

Shed roofs usually lean against a taller volume. If they don’t, they are subject to water intrusion on their high side. The Smart Houses addresses this with a short return roof on the upper shed that forms a ridge. Gable roofs, with two equal pitches are the most common roof form on the island but the construction challenge is in building the triangle above the end walls. Hip roofs are harder to stick frame and easier to build with trusses, which may not be an option on the island, but their eaves are easier to construct.

Because it is harder to build block walls on an angle (it requires a sloping concrete beam just under the raking eaves), block houses with gable roofs often frame this triangle in wood. Hip roofs have slightly more complicated framing than gables, but they have the same height walls all the way around the house and avoid this triangle. Occasionally there are hip roofs that lean, like sheds, against the end of a gable.

While pitches on gable roofs vary, lower pitches seem more common on current Nauru house types. Whitfield acknowledged the need for relatively low eaves but recommended higher pitches of at least thirty degrees, for cooling the interior. Standing seam metal roofs work at very low pitches.

Hip roofs perform better in very high winds because they are better braced on all four directions. Low pitch hips perform the best in high winds. Historically, this has not dissuaded Nauruans from using the more common gable roof form on modern era houses.

Water can be collected from any of these roof forms. Any roof form can be framed with trusses or stick framed with simple dimensional lumber. Trusses, which are made from very small stick members, are typically made in a modest plant. Trusses are engineered and the small members are held together with gang nails. Trusses can span greater lengths and their bottom chords act against the forces that spread a roof outward at the top of the walls and provide framing for a ceiling.

Stick framed roofs have to counteract the outward thrust of the roof by other means. There can be a structural ridge against which the rafters lean. This eliminates outward thrust, but ridges have to post at intervals where trusses do not. Posting a ridge affects the flexibility of the plan. The shed roofs of the Smart House have short spans supported at each shed by a structural wall running down the middle of the plan. If there is not a structural ridge, collar ties can counter the roof’s outward thrust.

In the U.S. even expensive houses can be built either with trusses of stick framed rafters. There is no common agreement about the right way to frame a roof. It still varies greatly by region. We build in a part of the country where carpentry skills are more limited but there is a thriving truss industry. If you stick frame in Nauru, you just need plans that allow for shorter spans, like those of the Smart House.

b) Eaves

Eaves probably pose the most complicated considerations and if window openings are the most expensive sub-assembly of a wall, eaves are the most expensive sub-assembly of the roofs.

First of all, consider the differences between the framing inside the walls and the framing outside the walls that form the eaves. You can form the eaves with an extension of the roof framing or you can attach a separate framing system that forms the eaves. Forming the eaves with an extension of the roof framing - especially if it is stick framing - is less expensive.

The argument against it is that if the eave starts to deteriorate owing to its exposure it is rotting a structural member too, that is more difficult to replace. Separate external framing systems can be scabbed onto the structural roof framing and replaced separately but attached rafter tails are more expensive.

Second consider the difference between an eave over a wall with a flat top and the eaves along the raking wall at the end of a gable roof. Most Nauruan houses with gable roof, extend the roof over the end wall to protect it from rain. This is appropriate but these raking eaves are more complicated to build. Typically they are built like ladders, half over the inside of the building and half cantilevered beyond the wall. The Smart House appears to build the raking eaves with extensions of their purlins.

There is a variant for block houses where the gable end is built of masonry, and running above it- a parapeted gable. This eliminates the cost of the raking eave but requires flashing where the roof framing meets this wall, and it does not afford shade of protection from rain. If this eave type is to be considered, there has to be a concrete rake beam formed at the top of the wall.

c) Eaves, Gutters, and Water Collection

A hip roof would have a gutter on all four sides of a house. A gable roof has gutters on two side. A shed is like half a gable and collects water on one side. Eaves help throw the roof runoff clear of the upper walls but they need to be detailed to keep water from running back along the underside of the assembly. This is done simply with a drip edge.

The high side of a shed roof, by contrast, is more prone to water running back to the upper wall, which is why the Smart House has a short return roof to prevent this. Alternatively, this is sometimes done with a parapet wall that goes above the roof. Generally sheds make more sense make more sense when they lean against a taller wall, like the lower shed roofs of the Smart House.

Eave assemblies need to be detailed to carry gutters. Gutters full of water tend to overturn and so an eave provides a supported vertical surface, a fascia, supported by rafters, from which gutters hang. The Smart House has a deep fascia than accommodates the minimal fall of the gutter required for the gravity flow of water

Gutters, downspouts and cisterns are elective costs, but the 2011 Republic of Nauru Census shows how common gutters are even now. The collection of rainwater will be an important means of decreasing dependence on desalinized water and so the upfront costs of gutters and downspouts will be recovered over a relatively short period of time.

d) Roof Ventilation

David Whitfield noted the use of ridge vents in some Nauruan houses but also noted complaints about wind driven rain intruding. He expressed the hope that improved vent systems would allow for the release of warm air and the protection from rain and insects. The Smart House has a ridge vent but no plywood deck.

We build in a saline environment similar to Nauru’s and there had been a protracted debate on advisability of venting the eaves, which can be more protected than the ridge. But the recent consensus is that vented eaves allow corrosive salt air into the attics that rust gang nails and metal tie downs.

e) Roof Insulation

Roof insulation, like wall insulation, is uncommon on Nauru.

f) Roof Sheathing

Typically a plywood substrate lends resistance to lateral wind loads and it provides a surface for a moisture barrier. The Smart House does not use plywood roof sheathing and it appears most Nauruan houses do not use a plywood deck. The housing committee says that plywood is rare because it is prohibitively expensive.

The 2011 Census surveys roof material on existing housing and metal roofs and asbestos roofs predominate. Asbestos is being removed. Concrete tiles are too heavy to ship. Clay tiles are brittle. Fiberglass shingles require a substrate. Metal roofs, whose panels work well with the typical rafter and purlin roof framing, come in a range of prices and materials. The most expensive metal roofs are very expensive but the saline environment will make less expensive galvanized steel options subject to more frequent replacement.

In a saline environment ferrous based materials like galvanized steel roofs should be avoided if possible. Aluminum roofs are available, but they are more expensive. Whitfield recommended them even 27 years ago when they were less common. In either material, simple lapped and screwed panels are less expensive than interlocking raised seam panels, but standing seams work on very low pitches. Metal roofing, according to the housing committee is shipped in coils and formed on the island.

4. Prefabricated Housing Versus Site Built Housing

Whitfield and Carstairs have a good extended treatment of the prefabricated houses that appeared in 1987/8. The even handedness of the discussion is something that distinguishes their entire report.

The housing was 111 to 121 square meters. There isn’t a reference to bedroom count like there is in the discussion of the earlier types 1 through 7. There were apparently shallow porches of 2 meters or less. This is interesting because the 2011 Census, for as thin as it slices housing issues, does not document porches.

The advantages cited for the prefabricated housing are the predictable ones of speed of erection and economy. The litany of offsetting problems is more fine grained. They are described as low and hot and the frames prone to rusting. They cited the use of foam sandwich panels. The report was written only a few years after the introduction of these units, but they express skepticism over the performance of the foam panels over time.

Whitfield and Carstairs are good on even the financial disadvantages of prefabrication-the cost of off island labor, the costs of shipping everything, even the lightweight frames; the cost of replacement parts and the labor to replace them.

The discussion of the Welcome House kits is instructive. Whitfield cites a cost per house of $90,000 or $740/square meter and says they were sold at a subsidized cost of $60,000. These numbers would have been from the early 1990’s. We don’t know the conversion factor into current dollars.

The Smart House program has an estimated cost of $3,000,000 for 20 houses or $150,000 per house. We don’t know if the basis of the Welcome House and Smart House is the same. But after accounting for inflation, it doesn’t appear that full upfront costs for the Welcome Houses reflected costs savings from prefabrication. The Island was wealthier in the 1990’s and we don’t know if subsidies will be in place for the Smart Houses.

Even before considering the benefits of island labor against off island labor, it doesn’t appear that the prefabricated kits of the 1980’s and 1990’s offered Nauru great advantages. In 2021, everyone agrees that the on island construction of Nauruans houses and the development of construction skills will be a key part of the island’s economy.

5. Overall Conclusions

The focus of this precedent study has been to understand how houses are built in Nauru. The next section will focus on how to program the houses.

While there is not complete agreement on how to build in Nauru the range of options is narrowed by circumstance and necessity. As we continue to work with the Steering Committee and the Housing Committee, we could focus a little more on how building might be different for the Higher Ground initiative.

At this point we don’t know how land for houses will be acquired or how mechanisms will be established for the transfer of ownership. Kate Fairlie on the Metrocology team will be working with the Steering Committee on these issues. We won’t know until the third phase of work what lot sizes are likely to be, or how security and privacy will be best served, but we will know soon and those concerns will be built into the first two phases of work.

We don’t know how houses will be financed. Housing programs in the past were heavily subsidized at a point when the island had greater wealth than it does now. We don’t know yet what this means, either. We don’t know if there will be multiple design options. We understand the Smart Houses would be built by multiple contractors.

The HGI is described in terms of sustainability. We don’t know exactly what this means in terms of the detailed construction questions addressed in this precedent study. In a narrow sense we could think of the issue in terms of energy savings, but all indications are that the climate is conducive to a lack of heating and air conditioning and that energy loss across the wall or roof or floor is not a big consideration.

Affordability seems to be much more important. Since it is more common to establish an affordable house size before thinking about room count and room size, it seems important to provide a broad range of house sizes and expansion options, so that home ownership might be maximized, regardless of income or means of financing.

The best way to think about sustainability probably has less to do with energy than about durability. Since World War II there have been a number of wood house types developed for the island but most everything argues against wood for the structures of HGI houses. There have been kit houses built off site and assembled on Nauru that are relatively less expensive up front but expensive to maintain and service, and everyone wants to use Nauruan trades to build these houses.

There is a preference for concrete slabs and concrete walls and natural ventilation, but the more durable methods of building cost more up front. If there are competing initiatives for HGI housing, there will be disincentives to serve durability through higher up-front costs. But

Nauruan homeowners will be best served by houses that last as long as possible and that are assets decades from now.

The policies that will serve Nauruan homeowners best will give competing parties incentives to all build to similar high standards of construction integrity. Financing mechanisms will have to ensure this because market mechanism alone won’t. As ever with housing, the challenge is to find the right balance between durability and affordability.