New Construction ro...
 

New Construction roofing question  

 

Matt T
(@Matt_T)
Advanced Member
Joined: 14 years ago
Posts: 261
June 7, 2017 11:32 am  

Greetings everyone!

I am in the process of building my own house. The walls are poured concrete. The roof will be a hip style which will have no overhang and be finished with a standing seam metal roof.

My question is related to sheathing over the rafters for the roof. I was planning on using T1-11 with the grooves facing down which is pretty typical here. I was going to paint all the rafters and sheathing before installation and would use a light color like an off white or sand or something similar.

Someone recently offered me some cedar tounge and groove planking at a really good price. Its already been on island for about 10 years and has been stored properly. Looks like very nice stuff.

For people who have T1-11 or planking for their roof, do you have any feedback on how its worked out for you? I could put the cedar to use for other things, don't necessarily have to use it for the roof but seems like it could add a nice aesthetic compared to the T1-11.

I know cypress is what's usually used and I would prefer the lighter look of whitewashed cypress but perhaps I could do something to lighten the cedar? On the other hand, I could keep it the natural color and just stain it clear and then use a cedar toned stain for the rafters. This would give a nice natural look that seems would be more maintenance free than something with a lighter color in regards to dust, mildew, etc.

Thanks for any input you can give me.


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singlefin
(@singlefin)
Trusted Member
Joined: 6 years ago
Posts: 913
June 7, 2017 2:51 pm  

I belive cypress is the wood of choice because it's naturally insect resistant. They used cypress T&G on my ceiling, over heavy 3" wide pressure treated rafters 24" apart. The contractor bolted custom steel brackets into the peak. We stained it a dark brown and I think it's probably the most impressive feature of the home.
I wouldn't have any concerns riding out a hurricane in it. No mold or bug issues since it was built 5 years ago.


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Exit Zero
(@exit-zero)
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Joined: 12 years ago
Posts: 2301
June 7, 2017 3:32 pm  

are you planning to have anything between the wood roof and the standing seam metal ?

Battens, insulation, sprayed foam for instance.


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Scubadoo
(@Scubadoo)
Trusted Member
Joined: 5 years ago
Posts: 2253
June 7, 2017 3:36 pm  

I've been looking at this site lately to compare wood properties. Apparently there are many varieties of cedar, which do you have? Some cedar is in the cypress family. Putting the rough side of T1-11 on the inside might make it a real pain to keep clean if you get any cob webs, bug dirt, a little mold on it. Paint may not smooth it out all that much. The cedar T&G is probably smoother?


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Matt T
(@Matt_T)
Advanced Member
Joined: 14 years ago
Posts: 261
June 7, 2017 4:05 pm  

Thanks for the replies so far.

Singlefin, yes cypress seems the go to here and if I was buying would go that route. But the cedar I am being offered is very good quality and price is right. I have also read that the cypress available these days is softwood and much more susceptible to rot and insects.

Exit Zero, I will have 1 x 4 or 2 x 4 purlins that the metal roof will attach to. I think I will definitely go with a radiant barrier but my research so far has shown that insulation does not make a noticeable difference on the roof, in particularly on houses that use natural ventilation for cooling. I am also aware that the air gap between the planking and the metal roof should provide a thermal break and help prevent radiant heat from getting through to the interior.

Scubadoo, thanks for the link. I am not sure of the type of cedar. I am hoping I can get more info on that. I do know that its about 10 or 12 years old and has been stored in a dry dark area. That means it has well adjusted to the climate here and I'm thinking the cedar that was available 10 years ago is probably better quality than what is being offered today.


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Jerry Barth
(@Jerry_Barth)
Active Member
Joined: 5 years ago
Posts: 16
June 7, 2017 4:27 pm  

Matt,
Are you committed to a metal roof? I was until Rolando Asencios of Asensios Construction talked me out of it. On his own Deltec house he simply put plywood decking down, taped the joints with fiberglass tape, primed it, then put something like 4 coats of this stuff called Top Coat on it. If you look at the roofs in STT there are a lot done this way. He also did a radiant barrier and regular fiberglass batt insulation. This would never work in Texas but if you think about it there's no hail problem and the temperature is fairly constant. Where are you building? For your cistern question I think I'm going to go with a pvc liner. Please PM me if you have any more questions.


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Matt T
(@Matt_T)
Advanced Member
Joined: 14 years ago
Posts: 261
June 7, 2017 4:52 pm  

Hi Jerry thanks for your reply.

Yes, I am pretty committed to a metal roof. I have seen many houses here with plywood roofs finished the way you have described. I am not keen on this for a few reasons.

First, I think you get better insulation from radiant heat by having an air gap between the metal roof and sheathing. With a plywood, the best you can do is paint white to reflect the UV.

Second, a metal roof over a sheathed or T&G planked roof is like a second line of defense. If you had a problem with the metal roofing, you have the tar paper barrier to prevent intrusion of rainwater. Also in a hurricane, I find it unlikely that a metal roof and its sheathing underneath would peel off, I would worry about this with a plywood roof. To me, this is where the tongue and groove planking is better than tongue and groove plywood sheathing, less of chance for it to peel off in heavy winds.

Third, I don't want to have to maintain a plywood roof. You have to pressure wash and re-coat every 5 years or so. I don't really like the idea of building up layer upon layer of paint over the years. I also worry about adhesion when re-coating and some of the paint flaking off and ending up in the cistern. I plan to use my cistern for drinking water as well so I want to keep it as untainted as possible.

An aluminum metal roof should last at least 50 years here with essentially zero maintenance.

I am familiar with the PVC liners for cisterns. I would probably hold off on doing this until several years down the road when my cistern may develop multiple cracks from seismic activity. I'm sure they are much more expensive than simply applying an impervious coating.


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singlefin
(@singlefin)
Trusted Member
Joined: 6 years ago
Posts: 913
June 7, 2017 7:17 pm  

Hey Matt.
I was told to expect between 20-25 years on the metal roof. Never heard of a 50 year metal roof, or for that matter anything built of anything lasting that long here.

😉


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SkysTheLimit
(@SkysTheLimit)
Trusted Member
Joined: 12 years ago
Posts: 1914
June 7, 2017 7:22 pm  

Matt,
You have obviously given this much thought and weighed some options.
Good job!

All I would add is T1-11 is just plywood run through a router setup at the mill. (But you probably know this). The grooves expose the layer's edges making for a rough surface in the grooves. I just built a screen room around an existing covered patio area and used T1-11 for the knee walls. You will need to prime and caulk the grooves where little gaps might have formed from knots or imperfections in the layers. If I were to use it for a ceiling I would want to sand every groove, caulk voids, sand again....... The roughness will attract dust, spider webs, dog hair, you name it, unless you can get it smooth. Pain to paint too unless you spray.

Alan
St. Croix resident since 2000


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Bombi/2
(@Bombi/2)
New Member
Joined: 3 years ago
Posts: 4
June 8, 2017 1:05 pm  

My roof is a layer of mold proof drywall over 3x8 Rafters, 2" urethane foam, 1" airspace with thermal barrier with 3/4" Plywood and a coated roof.
I recoat about every 3-5 years. It made it through Omar just fine. Should it ever become a problem then I'll consider a metal roof. In a tropical downpours there is very little noise.
Use the best corrosion proof fasteners.


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Alana33
(@Alana33)
Expert
Joined: 8 years ago
Posts: 12203
June 8, 2017 10:06 pm  

And hurricane clips.


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Scubadoo
(@Scubadoo)
Trusted Member
Joined: 5 years ago
Posts: 2253
June 9, 2017 12:32 am  

Hey Matt.
I was told to expect between 20-25 years on the metal roof. Never heard of a 50 year metal roof, or for that matter anything built of anything lasting that long here.

😉

I've seen 50 year or longer metal roofing available now. But it goes without saying make sure any metal roofing is properly secured for hurricane winds as well as the underlayment. Otherwise I could see it peeling up during a storm.


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