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Rastra construction / roof leaks

Posted by emmachas (My Page) on
Mon, Jan 3, 11 at 0:14

We would appreciate some insight or opinions from any contractor or builder who is familar with Rastra construction. A search of this site turned up very little. Nothing since 2004. A google search raised questions about possible water-proofing problems.
We're considering buying a 9 yr old Rastra home in New Mexico that has had several roof leaks all within 2'-3' of an outside wall. The foam roof was covered with Firestone membrane to repair. The leaks appear to have stopped.
Most of the houses we have looked at are about the same age and also have foam roofs but not Rastra walls. None of those appear to have had any leaks.
We like the house and the concept of Rastra. But can't shake the worry the leaks could be related to the Rastra walls rather than just a faulty roof.


Follow-Up Postings:

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RE: Rastra construction / roof leaks

How would ICF walls contribute to roof leaks?

It sounds a lot more like an inexperienced roofer or house designer.


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RE: Rastra construction / roof leaks

Thanks for the response, brickeyee.
It was my understanding---or misunderstanding, that Rastra differed from most ICF in that it had a great deal of pumice in it making it porous.
I'm sure you are right about the roof. We don't have flat roofs in our part of the country. Know zilch about them. It's been a crash course in building materials we are totally unfamiliar with----adobe, pumice, Rastra, etc.
I appreciate your insight.


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RE: Rastra construction / roof leaks

The best flat roofing material going remains EPDM membranes.

If you can get a piece large enough with factory seams (instead of field seams) all the better.

EPDM (Firestone is a very big maker) is UV stable, and used on large flat roof projects (stores, warehouses, shopping centers) in preference to the older built up (hot mop with multiple layers and gravel for UV protection).

Like any other roofing method, the biggest source of leaks are penetrations through the roof (plumbing vents, air vents, skylights, etc.).

The devil really is in the details of sealing penetrations.
Uncured EPDM is used, and the UV exposure finishes curing the material (and were not exposed it stays as sticky as anything long term).


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RE: Rastra construction / roof leaks

WOW, brickeyee!

Thank you for so generously sharing your expertise!

In a few sentences you laid out ALL the info I've spent 2 weeks searching for. Wish I had asked earlier!


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RE: Rastra construction / roof leaks

I have done some forensic examinations on the Rastra homes with leaks, it is not the roofing membrane that is leaking, the water intrudes through the Rastra and weeps under the membrane, Rastra needs to be completely sealed with a masonry waterproofing system similar Thoroseal before installing any windows or roofing. then there is always the posibily of cracks, which in turn an aquaseal addmix in the stucco, synthetic stucco,and or elastomeric paint should be used. this adds substantially to construction cost.


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RE: Rastra construction / roof leaks

Thank you for the insight and expert advice, Gene. This explains why the leaks were all within 2-3 ft of an outside wall. Closer examination of the house also showed water damage extending up from the floor about 2' along many outside walls. Had to be related to the improper sealing you referred to.
Thank heavens we decided against the house!
I'm glad your explanation will be here for the next person who does a Rastra search on this site.


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