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Robert Mace
Posted: Oct 26, 2013 12:04 PM
Spray foam on residential roof
I live in rowhouse that has a flat roof. I think the existing roof is hot tar over fiberglass. and it has been topcoated with aluminum. I am thinking of spraying foam over this existing roof, however I am getting different opinions on the foam. some people say that it is easily punctured by birds pecking at it. is this true? and can you apply the foam over the existing roof or does it have to be removed? does anyone have any experience spraying over hot tar on residential roof? thanks
Jesse Michalski
Posted: Oct 26, 2013 02:10 PM
In general , a foam roof is an excellent product. Yes, birds do peck at it occasionally. I've seen roofs with no bird holes, and some with several. You can cast granules by hand at an even rate and embed them into the topcoat that you go with and the birds don't like those if you are worried about birds.

I would just wait and see if they get to it. If they do, those areas are easily patched with an acrylic caulk product, like Kwik Caulk from Conklin.

Take a core sample somewhere on the roof and make sure you get down to the decking. From the core, try to identify the following things.

*Is the bond of the existing roof to the substrate or decking Sound?
*Is moisture present beneath the existing roof?
*are the existing materials and layers well bonded together or is there separation occurring?

If there is moisture under the existing roof, tear at least those areas out or consider tearing the whole thing off, make repairs as needed, and start over. I don't recommend trying to spray over a damp roof or you will have blistering, although many contractor's do this and it gives the product a bad name.

I don't think you would have any problem at all spraying foam on asphalt with aluminum, provided that the existing roof is a good substrate and well bonded. You should check with your foam manufacturer and ask their thoughts as well.

Make sure you have your local sheet metal guy fabricate a nice foam stop for the perimeter. Research foam stops if you are not familiar with the profile, as it is difficult to explain with words. This will allow for a clean and professional termination of the foam roof at the edges.

Just did a foam roof on an existing tar roof with gravel ballast. Removed the gravel, powerwashed, and found the tar to be well bonded. We experienced excellent adhesion of the foam to the old tar roof and it was a great finish.

The general rule with any spray applied product is that the adhesion is only going to be as good as the preparation of the substrate, so If you feel that the old roof is not a good substrate, go with your gut and tear it off. I would also power wash the whole thing and let dry prior to coating with foam if you decide to keep the existing roof on. The powerwash will reveal any loose material and expose any poorly bonded coatings, which will also help with your decision making.

Hope this helps a little. Good luck.
Posted: Oct 31, 2013 10:43 AM
SPF roofing is a completely different application than spraying foam inside a building.

KCfoam had some good advice. Here are some more things to consider

Check out SPFA's technical guideline on roofing AY 104, coatings, AY 102, blisters AY 107. It would also help to obtain the SPFA Certified Roofing Installer Manual and study it before doing any roofing.

My advice if this your first roof is to have an experienced SPF roofer work with you on the first job. This could be a suppliers rep, an independent consultant such as myself or another contractor who is looking for some fill in work.

Roofing has many challenges to address. For example bad weather (too cold, too wet, etc) can delay application for weeks. Remember you have to coat what you spray each day and to consider the dry and cure time of the coating. Most SPF roof jobs that fail are due to the applicator trying to stretch the application window. If you only have 5 hours to spray, don't try for 6.

Overspray is a big problem even a light wind can make the lightweight foam particles travel for hundreds of yards.

Penetrations and edge details are typically where leaks occur are particularly important to do right.

A flat roof still needs to drain properly so consider how you will be adding slope with the foam and getting the water off the roof.

Using the right coating is important, it should be suited for your climate and have a good track record of success in your area.

Check the adhesion of the aluminum coating to the roof, Many times the coating is flaking off and if you spray foam it sticks to the coating well, but blisters later when the coating continues to delaminate.

Don't forget about building codes, make sure the system (foam and coating) is rated and approved.

Happy to discuss this with you before you get in too deep. call me at 571-239-5221 or email masonknowles@aol.com
Posted: Jan 23, 2017 08:35 AM
I am looking to spray the foam over the roof and your opinions helped me a lot with this.I have discussed with my Roof Repair expert also and he also suggested to spray it without any tension.So thanks for the excellent information.

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