Monday, October 8, 2007

Details and photos of residential flat roof in action

Some folks have asked us how the roof will be constructed, since there aren't too many of the flat roofs on houses around here. Well, you actually do see them everywhere, but they are found on commercial buildings and according to the roofer guy we talked to (Pepe at Pro-tect Roofing Services), they are much better made and last 5 times more than the conventional, heat absorbing dark gray asphalt tiled roofs. They are a little more expensive to build, but not enough to offset the energy efficient and durability benefits of this roof. I will post prices once I get them from Pepe.

I was lucky enough to be able to get on top of a roof while it was being done. Pepe let me see his work and he's a prospective roofing sub that we want to hire. He was very knowledgeable, as well as nice and helpful and not condescending like many of them can be - especially to a female. He wanted me to witness his workmanship in person, which says a lot about him. Anyway, I took some photos to help you understand how this will be done (and it WON'T leak!). I took some pictures of the roof he's working on (not our house in these pics, sorry!). This is called a commercial grade, residential flat roof/low slope taper roof system using a single-ply membrane:


First, our roof will be an 8.5" SIP panel (foam sandwiched between OSB wood boards, see earlier post about this), then styrofoam wedges (see A) are attached to the SIP that will give a pitch or slope (see B).

The Tyvek house wrap goes above and over the parapet wall (see C). Then the single-ply membrane is rolled over the styrofoam wedges and attached using screw attachments (see silver round attachments in D-E). Pieces of the membrane are layed up on top of the parapet wall (see H on the left parapet wall) and also cover the screw attachments (see E) and then roofing adhesive is used to adhere the membrane to the parapet (see F-H). Finally, all edges and seams are heat-sealed using this hot melding tool (see I, sorry, I don't know the official name of this thing!).

It has a 1/4" slope for every foot, so it's VERY gradual, but enough to drain out the water on the roof. Since we are doing rainwater collection, this is very important and the single-ply membrane must be safe for drinking water. We found a really good brand called Duro-Last that is a reinforced polyvinyl chloride polymer and comes in 40 mil and 50 mil thickness, which is safe for rainwater collection. If you go on their website, there is a lot of technical specs for those that need to know the chemical makeup and information on finding a contractor near you.

If you look carefully at the far edge (click on the picture to enlarge), you can kinda see the low slope in the following photo. Also, we will have a much higher parapet wall then this house, but it gives you a good idea:

Pepe says this is a superior construction to using tiled roofs. The ceramic tiles you see on Mediterranean homes are VERY expensive and high maintenance, and this one in comparison is very low maintenance and lasts 5 times longer. Not only that, but the foam adds added insulation to your roof (even if not using SIPs) and the white or light colored single-ply membrane reflects a lot of heat giving you a very sweet, energy efficient home.

Here's a pic of how it looks on the side of the house (see A) and see how nice and clean it looks, as you don't see an ugly roof when you look at the house (I am biased towards not showing roofs, and don't care for the A-line/many gables look). Also look at how creative you can be with the underside (see B) of the roof, by adding lights or wood siding to give it an architectural element.



You can also mount solar panels on here as well as have rain water collection, adding to the greenness of your home. Note that if you do add solar panels, make sure a professional roofer is on hand with commercial experience to seal the attachments of the solar panels with the same method explained above with the parapet wall. You don't want your single-ply membrane to be punctured or damaged!

20 comments:

Anonymous said...

Ok. That looks interesting but I'm a little confused. Here is my interpretation of the A-E pictures:

Picture A is a piece of the Styrofoam.

Picture B shows a piece of the membrane on top and installed Styrofoam on the bottom.


C is larger scale showing installed Styrofoam to the right and the whiter membrane to the left.

D just looks like membrane coming into the parapet wall. I don’t see Tyvek on the roof here.

E looks like Styrofoam on the roof deck and Tyvek on the parapet.

Please correct any mistakes. Also, what are the round things all over the (what I think is) styrofoam?

I plan a flat roof but I'm using roof trusses. The trusses can be ordered with the slope engineered into the truss. Can I just add the membrane? Thanks for any thoughts.

-----
Bob

Anonymous said...

Oh one other thing. You refer to the top layer as a "sinle ply membrane." Do you know what this is made of or how thick it is. I was wondering how I would specify it if I wanted it on my flat roof in NM. Thanks. I really enjoy your blog.

Myleen and Jan said...

Hey Bob, glad to see that you are keeping me on my toes at all times. :-). It is fun, as a woman, to be technical with our building process, I'm learning a lot! I work as a Technical Writer by trade so I have to be very correct anyway and this is good practice. But, I appreciate you making me clarify the picture! I have now corrected the picture and description, and if there's still a question, please comment again. You should check out Duralast (link on the blog) for this single-ply membrane and make sure your roofer has commercial roofing experience.

Myleen and Jan said...

Oh, and to answer your other question about the sloped truss, how are you insulating your roof? I would think that the styrofoam would give you added insulation and maybe you can order those without a slope and follow your truss slope instead? I would definitely ask the roofer, but I think having the foam there would be a good thing for you. Hope that helps. I'll ask my designer if he has any thoughts and post.

Anonymous said...

Thanks for the revision. I'm clear now.

I don't know how I'm insulating the roof. I'm not going the owner-builder route, but my builder is very interested in green building. I had a discussion with him about the roof trusses but I did not get into exactly how we're insulating.

Flat roofs are very common in New Mexico but residential roofs are typically built up asphalt roofs (BUR). Do you have any sense of the cost differential between BUR and single membrane commercial roofing?

----
Bob

Myleen and Jan said...

I don't have any exact figures, but the roofer was saying that the single-ply membrane commercial roof does cost a little bit more to do compared to asphalt, but the savings associated to lower energy bills should pay off the higher cost. If you look at the post before this one called "Natural stucco, wood siding, our masonry...", that house did something different, by placing darker gray asphalt on top of the slanting SIP roof. I suppose since it is insulated in SIP, the dark asphalt would not matter, but realize that the if you didn't have that foam insulation, your roof would soak up more heat. From what I heard from various people, ICYNENE (spray foam) and batt insulation are not as effective as the styrofoam insulation and you should find a way to use a radiant heat barrier (for example, radiant heat barrier paint, light color membrane or metal on the roofing) as well as insulation to increase your energy efficiency of your roof, and since you are NM, I'm sure you'll get plenty of sun on it!

I think it's great that your builder is interested in green building! The more the merrier is how I see it in this industry! But as the home owner, it's always advisable to be just as knowledgeable and current to building as the builder him-herself. Good luck with your house project and please keep the questions coming!

Anonymous said...

Good JOb! :)

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Unknown said...

Nice photos of the house and its roof. That was so interesting to know. One of my friend suggest a Roofing company from which I have hired the roofing services. Really they have done a great work for a affordable price.

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Commercial roofing Pittsburgh said...

Roof construction is indeed a one great task to fulfill in some future time and in the right way. This serves as an example of its effectiveness.

Brendan Gertner said...

First of all, good choice picking a flat roof. Your roof guy is right: this type of roof lasts longer. But just like any other roof types, the duration of flat roofs is based on the homeowner's regular inspection and maintenance.

Unknown said...

keep me up great work thanks for sharing.

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Extruded polystyrene said...

I installed the Extruded polystyrene that carries an R-5 value for 1" and it has made a tremendous difference on my basement walls. I have a walkout basement, so it is more subject to the temps outside than an in-ground basement.

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I was wondering how I would specify it if I wanted it on my flat roof in NM. Thanks. I really enjoy your blog.
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