Concrete roofs and roof patios in the Philippines?

A flat concrete roof for your Philippine house?  Here are a few things you should consider.

Lovely roof patio

The flat or nearly flat concrete roof is an irresistible draw.   It vastly increases living space at a little more cost than a conventional metal roof.  It seems unlikely to blow off in a typhoon. But, most appealingly, the  flat concrete roof can be used as a high patio with privacy, breezes, views and so forth.   If you do decide to have a concrete roof, I suggest you support the concrete using galvanized steel deck forms.   These metal panels look something like galvanized roofing but heavier.  The panels serve as a permanent steel base for poured reinforced concrete floor slabs. The need for temporary wood forming is eliminated.  The panels are supported by the concrete beams.

Floor deck forms for a concrete roof.

The concrete roof is appealing idea but we advise caution. The sun will heat the slab all day and then re-radiate the heat into your house 24/7. We have a friend who built a house like that with the idea of using the roof as a patio. The house was pretty much an oven and the patio unused.  Most of the problems can be overcome but with additional expense.  The patio can be roofed or partially roofed to give some shade both to people and to the roof itself.

An insulated ceiling can be installed below the roof, but these add to the already high cost of the concrete roof.  There is no ameliorating the fact that having a slab of concrete high up in the house is a hazard in an earthquake.  Not only could the roof come down on the house inhabitants below, more importantly the tons of high-up weight can magnify the pendulum-like lateral sway of the entire structure, especially in a multiple-story residence.   If such a roof is decided on, be sure your engineer designs the structure below to accommodate the additional stresses.

Comments (22) Write a comment

  1. Thanks for your blog. I was looking for information for some steel trusses construction for my patio and shed. I built it with wood and polycarbonate roofing but it quickly deteriorated (3 years). So much for that 10-year warranty they gave on the polycarbs. I am basically a DIY woodworker but trying to learn steel construction these days.

    Anyway, just to add here, I had my house constructed with a concrete roof deck (120 sqm area which is the footprint of the house). Cost was almost similar to a shingle or clay roof (which is the only roofing allowed in our subdivision). I did not skimp on the rebars and used 12 meter long span grade 60 #12 rebars for the beam and slab with top and bottom reinforcements. I had the concrete poured and used the vibrator.

    I did not finish the top and for the last 5 years, no leaks were experienced. However, just last month, some water developed inside so probably, either this was due to the concrete degrading already or the constant shaking here in Cebu. So no other choice but to waterproof. My plan is to use “rubbercoat” by Campbridge which looks good on paper and topped with concrete with cementitious waterproofing additive. It will be painted with a waterproofing paint, so thats 3-layer overkill. :-)))

    http://www.campbridge.com/RubberCoat%20Technical%20Info.html

    I dont have a ceiling (10ft height) so yes, it was very hot during summer. However, the solution was just installing 4 x 12″ exhaust fans from the inside. After 15 mins, the house gets very cool. I also close my curtains everytime I leave the house to minimize the sun hitting the inside. I am keen to try this “ceramic” paint from the same company as above and see if it helps.

    http://www.campbridge.com/Ceramicoat%20Insulating%20Paint%20Technical%20Info.html

    Reply

  2. hi there,
    we live in taytay, rizal. we are planning to build an additional 2nd floor with a concrete roof not for patios but for safety reasons like floods. a lot of our neighbors have concrete roofs replaced the old roofs they have maybe witht he same reasons that we have.
    can a foreman built it or do we have to ask for an engineer or architect? budget is quite tight now so we need to know the best and cheapest way.
    hope to hear from you soon.

    thanks.

    jj.

    Reply

    • We suggest discussing your ideas with a competent engineer. Your neighbor’s concrete roofs may be fine, until and earthquake comes and the roof comes crashing down.

      Reply

    • Hi JJ.

      I suggest if you can consult for a Licensed Arch. or Engineer, this will give you an idea on how to Build the Roof Deck and probably will give you suggestions on the specs. of materials to be used and possibly for a lesser cost because they knows best. Consider adding weight on the existing structural columns you have will increase stress on this supporting features, its best to seek assistance to them to assess first your house.

      Reply

      • thanks for the reply. the first cosultation is usually 5k and its for visit and they require 3 visits so that is 15k already. its too much for us specially now that my father has lost his job. so i guess we have to brave the floods again this 2014 season.

        Reply

        • Hi Aries, the standard dimension to support a 4″ hanging slab is an 8×8″ concrete column with 8 pcs #12 reinforcing bars on a 24×24″ foundation. thats how the houses are usually built here. standard distance between columns is 10′ (ideally with tie beam underneath). if you have those, then you can specify a 4″ slab with a 12″ beam underneath. there is a book about reinforced structural concrete (about Php 180 in national bookstore) that’s aimed for non-engineers. i had my plans built by my cousin but was relying on the book the whole time. no visits were necessary. my house is 2 floors with a 115 sqm concrete roof deck.

          Reply

  3. Hi Bob

    Roof patios is ok and nice but build with a thoughtfull mind. Take a carport, or an open area for car parking and like this, build a roof and patio on top of that, and you have an extended area which is safer than on the ground against intruders.
    Then make a “tant” or a big umbrella to shade there so the persons using it is in shade and can enjoy wind up above the ground.
    Against weight and height, which during earth quake is making it worse, Make the concrete thin, and hollow, or with channel plates underneath as your sample shows. I see here, they use “Bubblenet” which is prefab reinfroced net 2 layer with plastic ball trapped between the layers in the square field made by the steel rods. Its anyway only the upper level of the concrete that is used to take pressure, where the strength is done by the reinforcement in the underside. This makes the concret typical only half the weigth.
    Another thing is, that using EURO norms for this, a 80 mm layer is fully able to take the load of a normal living place, and that can even be in fields where there is 300 mm between reinforcement so it can bo vafled un the underside to minimize loads as well. and / or, a layer of EPS can be included on top of the bottom layer of concrete, and a layer of concrete on top again, where the 2 layer of reinforcement is strongly tied together with steel hooks, complicated but possible.

    Then the alst thing, the diagonals needed to prevent pendulum swing. It dont have to be underneath between the coloums, but can be on top as a wall along the sides of the patio, it just have to be done properly to stabilize this. Even off cause, the best diagonal is done below the deck.

    Regards.

    John and Racel

    Reply

    • John,

      Good to hear from you again! You mention using umbrellas and tents on roof decks, but what I see here very frequently is people building bahay kubos (bamboo native houses) on their roof decks. It seems like a great idea to me. The bahay kubos are cheap, can stay up during storms and provide a cool and breezy place for a siesta or to watch the sunset. I’ll take a photo of one of these and post it.

      Bob

      Reply

  4. Great article.

    i have a 6″ concrete poured slab roof on my PI house, and I tell you – it’s amazing… Keeps the house dramatically cooler during the day, and almost no sounds get through from the outside world (radio, roosters, trikes). I also (like you said) have a great roof deck for parties.

    You can get some fairly inexpensive block foam if you want to put it on the inside (and a drop ceiling) to further insulate, or you can have a hard foam on the topside. I have neither and have no issues.

    One problem of course is occasional leaks where builder joined slabs (doh!) the roof paint just doesn’t work for more than one season – will try advice above and go for epoxy paint.

    Reply

    • Ghost,

      Many thanks for your report. It’s always great to hear from people with real-world experience.

      Bob

      Reply

  5. Your comments are fairly interesting about a concrete roof. Properly designed, it is not much different than having a second story house.

    Here in Korea, a flat roof was the standard back in the day. I bought a house a few years back that has a flat roof and I absolutely love it. The house is almost 40 years old and there are no issues with leaks (though you need to repaint with epoxy paint every 5 years or so).

    Granted Korea only has a couple of months of terribly hot weather, but we also have the extreme of the winters. I gutted the house down to concrete and studded everything out and insulated and have had no issues.

    Since I plan to use a similiar style when I build my house in the PI, I guess I need to look into it a bit more.

    I definitely agree about using steel deck, it is a great product but need to research how easy it is to get where I plan to build.

    Thanks for a great site, I have really enjoyed reading about your home construction.

    Reply

    • Shawn,

      Thanks for your very helpful comments. They are a good antidote to my opinionated comments about concrete roofs. What you say makes sense. If the interior is insulated, the concrete should be fine. What will you use for studding, insulation and interior walls? I would really fear rapid deterioration in this climate. Perhaps steel studs, foam insulation and Hardiflex?

      Bob

      Reply

      • Bob,

        Actually my plan for the exterior walls is to use 4″ block and 4″ styrofoam on the exterior and then just plaster over it. I think that will give a decent insulation value and it is easier to “channel” through styrofoam for water lines than filled CMU block.

        For the ceilings I’m planning on a suspended metal system with cementitious board, tar paper for a vapor barrier, mesh and then plaster over the ceiling. Also using batt insulation. I just need to figure out if they have cementitious board or if I have to use hardiflex. I’m not familiar with hardiflex other than what I have read, but is seems to be similar.

        Shawn

        Reply

        • Sounds like a good plan. Hardiflex started out as an asbestos-cement board, but now uses some sort of wood fiber in place of the asbestos. All of our ceilings are Hardiflex. Some use thin plywood for ceilings, but I was advised to use Hardiflex and am glad I did. Much of the available plywood is really poor quality.

          Reply

    • I’m also really interested with solid poured concrete roof. I’m trying to research what are the best thing to do specially for leaks. I’m from Davao City planning to build a single floor house. I thought this is the best possible design to a so called “minimum maintenance house”.

      Reply

  6. please respond i am very very keen to establish a earthquake resistant 6 inch block design for the areas Manila as a professional engineer and builder using mortarless core filled block supporting solid in situ concrete bond beams from lintel up to top plate for a roof covered in highly reflective painted metal sheeting on light weight steel trusses. I am calculating if cable diagonals saw cut into the finished block and anchoring each top corner to the floor beams will enable the whole slab and footing to be out of the ground as a raft slab and shear across the surface for the severe cases of soil spread and provide a flood level buffer at slab level because of the slab thickness above natural ground level..The design is for a modular low cost 5m by 5m box design house suitable for one phillipino family of 4 to 5 persons..can you assist with any photos or contacts on your island or another nearby island that have done similar or people I can correspond with who are as wonderfully (if only we had done …)honest and inquisitive about structure and function with a single skin fabric in concrete and steel as you marvellous people present yourselves to be. Costs from phillipines material cost indexes 2011 suggest a finished box with eaves at under 300/sqm (metric) or $280 a sq yard (US) or 3100 for 100 sq ft
    I am hoping to visit the place in april May 2012 ( not typhoon august thank you) and tie in the work on 10 to 12 of these on church grounds as a charity job because when the big Richter does come I want something to be still standing albeit a little further away from its original site…. looking forward to your most enjoyable style of reporting if you can spare a reply

    Reply

  7. Thank you for blogging your thoughts, experiences, and knowledge while building your house, specially in the local context. I am likewise embarking on my own project and I cant wait to get my hands dirty – secured with the knowledge shared thru your generosity, I am sure it will save me a lot of grief and remorse once my house is done. Thank you!

    Reply

  8. Pingback: Our Philippine House Project – Roof and Roofing | My Philippine Life

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