What we’ve learned about roofing systems, roof trusses, roofing materials and cost of roofing in the Philippines as part of our house building project.
Roofing systems have become very standardized in the Philippines. What we describe here is the roof system that goes on most houses except the very high end such as real clay tile or cement tile, a few asphalt shingle roofs and the Nipa or sheet steel roofs of the ordinary “bahay” – native house.
Concrete Roofs. See THIS POST
Metal Roof Basics. Steel trusses of various designs rise from the topmost concrete roof beam. The trusses are welded to stubs of rebar protruding through and well anchored in the concrete roof beam. (One reader suggests that this is inadequate. See comments below)
The trusses are almost always welded-up on-site and then primed. It’s best to use one of the two part epoxy primers, especially if you’re anywhere near the sea. We used Boysen Red Oxide Epoxy Primer which we bought from Iloilo City Hardware on Iznart Street in Iloilo City. The cost was P603 per gallon. You get two cans per gallon, the primer and a smaller can of hardener. You’ll also have to buy epoxy reducer, an expensive thinner for epoxy. The reducer is about P420 per gallon. Some of my crew members tended to waste the reducer, especially trying to clean brushes. Finally, I learned to buy cheap brushes which could be discarded. Once the hardener is mixed into the primer, it very difficult to clean brushes. There are cheaper epoxy primers, but we’re impressed with the Boysen.
Metal trusses of of various designs rise from the roof beam which top the hollow block walls. The trusses are welded to stubs of rebar previously embedded in the roof beam for that purpose. This system seems to work. We did not see any roofs of this type blown off during Typhoon Frank in Iloilo City. Here you see four 12mm rebar wrapped around the truss and welded in place. They will be painted later. In total, the roof is held on by at least thirty such rebars.
Our roof trusses were a bit unusual. Most trusses use the interior walls of the house for support so that the spans are shorter. This requires less steel and saves money. Our trusses were designed so that they could span the entire house without support — sort of like what you’d see in a basketball court or warehouse. This would allow us to have quite a lot of open space in the attic, although we never requested this and are unlikely to use the attic space.
The center girt is 40cm wide and is welded up from 2″ x 2″ angle bar, 5mm for the frame and 3mm for the webbing. The 35cm wide rafters use the same angle bar.
Originally, the height of our roof from the top of the wall to the peak of the roof girt was to be 2.5 meters. We put up the center girt and two rafters and the roof pitch just looked too low. On the spot, we decided to increase the roof height to 3.0 meters This what’s possible when you’re running your own crew, but such decisions, if they’re not carefully thought out, can have ramifications you’ve not yet imagined. In this case we seem to have gotten away with this snap decision. Of course the steeper roof meant more roof area and more roofing materials.
Once the trusses and or rafters are in place, a system of lightweight steel purlins are installed perpendicularly across the rafters. The purlins can be initially first pop-riveted to the rafters, then when the all adjustments have been made, welded to them. These are our 2″ x 3″ 1.2mm roof purlins. They all have to be painted with epoxy primer. We paid P400 each for them in April 2010 but steel prices are going up rapidly. Our roof needed 85 of these purlins. They are spaced between 50 and 60CM apart. You have to be very careful when shopping for purlins to make sure the material is not substandard in thickness.
This photo shows the purlins installed across the rafters (trusses). The photo really shows all the elements of the roof structure; the 40cm center girt at the ridge, the 35cm rafters, the collar beams and the purlins. Next comes the facia and soffit frames.
The purlins support the long span steel roofing, but before the roof itself is put on, a metal ”facia frame” is installed around the perimeter of the roof. Our frame is welded up of 1″ x 1″ angle bar and 1″ flat bar. This frame supports and is hidden by a metal facia “board”. The facia frame may also supports the soffit. At the rakes, the facia frame is welded to ends of the purlins. At the eves they can be welded across the rafter tails. The facia frame is the structural heart of the Philippine roof cornice system.
This is a photo of a very simple roof. It shows the scalloped prefabricated steel facia, the prefab gutter attached to the facia and the red oxide primed purlins supporting the unpainted galvanized roofing. On simple buildings like this one, pop rivets hold things together.
Once the purlins, facia and soffit frames, facia board and gutters are in place, the long span roofing can be screwed to the purlins using self-tapping tek screws. This is usually done by a crew working for the company which sells the roofing. ”Long span” means that the roofing sheets are long enough to reach from eave to peak without joints. Once the roofing is on, the matching ridge caps and any other accessories go on.
This photo shows the soffit frame (below) and the facia frame. The soffit frame is constructed of 1½ x 1½” 1/8″ (2mm) angle bar. This angle bar is P305 for a 6 meter length. It’s cheaper than wood. We used a 60cm x 120cm framework of this angle bar for our entire ceiling structure.
To recap; a system of lightweight steel purlins are installed perpendicular to the trusses. The purlins provide support for the long span steel roofing which is screwed to the purlins using “tek” screws. The other parts of this standardized system are a steel frame welded to the ends of the rafter tails. This “facia frame” extends around the entire roof edge. A pre-painted steel facia “board” is attached to and covers the facia frame. Then pre-painted, decorative gutter is attached to the facia board. The installation of the facia frame, facia board and gutter allow the tweaks and adjustments so that the final roof installation can proceed smoothly.
These roofing systems are generally available in .4, .5 and .6mm thickness. Generally .4mm is used as it’s the least expensive. We originally ordered .5mm for the roofing and .6mm for the gutters but it was not available so we had to order .6mm at a considerably higher price. This has proved to be a blessing. If you can afford it, the .6mm roofing is very worthwhile. The .4mm roofing is rather easily damaged by workers and ladders and rusts out more quickly. Our roofing is said to be “Galvalume” coated, that is coated with a mixture of aluminum and zinc which is supposed to be more durable than ordinary galvanized steel. Supposedly the paint is applied in a Taiwan factory. This 6mm material is widely used in roofing commercial buildings. Update June, 2010. After two years we do not see the slightest sign of corrosion.
Insulation. Metal roofs are notorious for turning your attic space into an oven. It’s fairly common to install a thin foil-faced foam insulation under the roofing to try to reduce heat transfer. We were dubious about the durability of foam under such extremely hot conditions. We also wondered if so much foam could be a fire hazard so we decided to use foil-faced 25mm fiberglass instead.
The insulation, foil face up, is supported by a network of 16 gauge galvanized “tie” wire. Holes are drilled in the purlins and the tie wire in threaded through the purlins. The holes are positioned so as to leave a 1/2″ air space between the foil and the underside of the roofing. This spacing improves the reflective properties of the foil.
The roofing is available in a range of colors. We’re using a light color. See this New York Times article on how white roofs save energy. Dark metal roof colors are quite popular in the Philippines, we guess because they give the look of clay tile roofs.
Now that the roof is on, the house looks a bit like a Philippine basketball court. The interior walls are 3.4 meters above the finished floor. It’s another 3.0 meters to the roof peak. The total height is about 20 feet. We could have spectacular cathedral ceilings, but will likely install ceilings between 3.2 and 3.4 meters above the finish floor level giving us a 10 foot ceiling height. Even then, changing light bulbs and cleaning ceiling fans will require a high ladder! The ceilings will be supported by ceiling joists of 1.5″ x 1.5″ 2mm angle bar.
This photo also shows electrical conduit running from outlets to the panel box. The concrete floor will be poured over the conduit.
The design of our roof includes two large vents high in the roof. More on that later.
Material options for the soffit include pre-painted, ventilated steel soffit packages, Hardiflex brand cement board and plywood. Since we’re trying to give our house a bit of a traditional feel, the metal soffit system, while very practical, are a little too reminiscent of a mobile home. Hardiflex appears to be similar to the asbestos-cement board we used to see, but the asbestos has been replaced with wood fiber. We decided to use painted 1/2″ marine plywood. The plywood is referred to “11mm plywood” but actually measures 10mm. Since a hole punched in the soffit can open up access to the building, we felt that plywood was a more secure choice than the brittle Hardiflex. The plywood is attached to the steel soffit frame with 3/16″ blind rivets. The rivet heads are recessed and filled. All surfaces of the plywood are primed before installation.
Note that, except for the plywood soffits, not one bit wood is used in the entire roof structure. Termites are a part of this, but Philippine forests have been almost entirely cut off and wood is quite expensive.
Cost. The surface area of our roof is about 300 square meters. The total cost of the roof excluding the structural elements but including insulation and installation is about P280,000 or about P700 per square meter. The fiberglass insulation added about P50,000. We were told to expect to pay about P500 per square foot for our roof but using better materials drove the price higher. We have not yet calculated the total cost of the roof structure plus roofing but it must be at least P800,000.
We purchased the roofing from and it was installed by Far Eastern Hardware, 38 Quezon Street, in Iloilo City. We dealt with Victoria “Baby” Ang. When our plans were found not to be complete enough for our crew to build the roof structure, Baby sent an engineer out to help at no charge. Land line phone for Far Eastern is +63-33-337-2654. Mobile for Ms. Ang is+63-918-888-2228. Getting through can be a challenge. Ms. Ang is quite business-like. One time she failed to give us the usual friendly greeting to us as we walked in to negotiate an order for more building materials. She joked, “if you want friendly, go to Jolibee” and laughed. Our business dealings with Far Eastern and Mrs. Ang were always straightforward and satisfactory.
Summary. All parts of this Philippine roofing system are matching; preformed and pre-painted so that the entire ensemble of roof panel, gutter, facia board and ridge cap are in the same design and color. This is a very slick, economical and attractive system which provides a durable roof able to withstand the monsoons, typhoons, termites and other rigors of life in the Philippines at a moderate cost. We’re impressed. My only reservation is that roof sealants (Elastaseal, Vulcoseal etc.) seem to be an accepted part of the Philippine roofing world. I have some experience with high quality metal roofing on U.S. historic restoration projects. I consider the use of these sealants to be a bad sign. These sealants always fail. A roofing system that depends on them is poorly designed and will require frequent maintenance as the sealants break down. Our rental apartment has a metal roof. Whenever there’s a strong rain, it leaks and the landlord sends a crew with tubes of roof cement to try to repair the leaks. That’s not how I’d like to spend my retirement! A properly constructed metal roof will use proper design, not sealants and will be leak free for decades.
Here’s a little about the architectural design of our roof. Our roof design goes against the trend. Increasingly elaborate roof designs are very popular, especially for houses that are or aspire to be “upscale”. The more valleys, ridges, dormers and other complications the more impressive the house. Bob was brought up in the northern U.S. where every valley was another spot for ice and snow to build up and cause ice dams and leaks to form, so simple roofs are an instinctive choice.
These over-complex roofs are a recent development in the Philippines. Traditional Philippines houses had “dos aguas” or “quatro aguas” roofs. These terms are a carryover from the Spanish “un tejado de dos aguas”, a simple ridged roof or “un tejado de quatro aguas” a hip roof. The older members of my construction crew still understand and use these old Spanish terms.
The hip roof has been very popular in traditional Philippine buildings and for good reason. In a land where buildings are buffeted by typhoons every year, the hip roof is streamlined, giving the winds little purchase.
The roof above was popular in the 19th century but during the Commonwealth era one starts to see a modification which adds roof vents.
In Western architectural lingo such roofs are called “gablet” roofs or “Dutch gable” roofs.
Certainly the aesthetic for this roof is inspired by the roof profile of the beloved Philippine “bahay kubo” native bamboo house. Filipinos, rich or poor, seem to have a deep attachment to life in the provinces. For Filipinos, the provincial life and the bahay kubo conjure up an idyllic paradise lost. Of course Filipinos know about the hardships of provincial life, but those don’t seem to dilute the romantic attraction of life in the provinces. Just consider the current crop of TV soaps which alternate between a sorid, squabbling life in huge, pretentious houses in Manila, lives filled with greed, envy and bickering. Then in a flash you are in the provinces, in a bahay kubo,maybe with some pretty capiz windows–a harmonious pastoral life populated with kindly, wise lolos and lolas with birds singing and maybe a carabao contentedly ploughing in the background!
This rustic bahay kubo roof design, transferred to wood frame and concrete buildings, has evolved to incorporate a ventilator in the peak of the roof. We wanted to incorporate at least some Filipino style into our house and also realized the advantages of attic ventilation under our hot metal roof. Here’s our original design for a two story house.
We finally decided on a one story home but kept the roof design we liked so much. In retrospect (5-12) this was probably not a good decision for our very exposed location. Storms blow water through the ventilators onto the Hardiflex so we have had to block off the ventilators. Readers have recommended that we install storm-proof ventilator grills. We shall do so but our attic ventilation is adequate without the vents at the peak. Including the peak vents added complexity to the construction, cost quite a lot of extra money, will require maintenance and really provide little or no benefit. The low pitched hip roofs seen on many Philippine houses are practical and affordable.