ISO Board on Roof? Remove membrane or place ontop?

Hi: I am getting my roof re-done and was told I can place the ISO board ontop of the old membrane then attach felt and rubber over that. The old membrane is not in the best shape and fairly uneven. I am wondering if I should strip to wooden deck and apply the ISO board directly over that. I am planning on 4 inches of ISO board. Anyone do this recently?

misconformist

in Roofers 11 years and 4 months ago

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daintydu | 11 years and 3 months ago

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Johnife – can you email me? I’d like to ask about your contractor and a few more details about your process. We may be in the same boat. Thanks. Daintydu at gmail

deanbh | 11 years and 4 months ago

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Do you have photos of the iso board you installed? what brand did you use? We’re needing to sort out some “sagging spots” in our co-ops roof and and thinking of using isoboard with attached OSB to help this problem. Who did you use to do this?

evperry | 11 years and 4 months ago

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Strip to the bones and redo it the right way. Flats roofs LOVE to leak if done wrong. New plywood, flashing and coating will give you a nice 10 years leak free. Make sure the guy you hire is licensed in NYC as a HIC. This is VERY important. You will save yourself headache.

johnife | 11 years and 4 months ago

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After having a new membrane put on our roof a few years ago and suffering leaks again within three or four years, we had the roof on our 21ft x 45ft brownstone stripped to the boards last year and totally re-roofed with 3in of insulation, SBS-Modified Bitumen membrane and including replacing three skylights, a new Bilco roof hatch, and all new flashings. There was about a 1″ thickness of existing roofing material there, partly tar, partly built-up roofing membrane. I took a sample to a lab in Manhattan to have it tested, fearing the presence of asbestos content beyond the permissible percentage, and my fears were confirmed. Since I was now going to have to deal with a licensed asbestos abatement firm, as well as a roofer, and a mason because 3 chimneys needed to be re-built, I opted to go with a GC to handle the work. The option of not acknowledging the presence of asbestos and trying to get the roofing removed “under the radar” (a fairly risky thing to do anyway IMHO given the horrendous fines you will be hit with if discovered) was totally out of the question given the past unfounded DOB complaints about other work on my house by a bitchy tenant in the house next door. Dealing with the asbestos (decontamination tents in the back yard, workers in protective suits and masks, air testing etc.), including its proper disposal, added a LOT of money to the job. The whole project cost $40k including around $16k for the asbestos premium and $6k for the chimney work. Despite the cost, I’m glad I did it in what I consider to be the right way. Zero leaks so far, even with the melting snow, and a 20 year warranty which would have been impossible to get without a strip job. It’s also worth noting that none of the reputable roofers I contacted before the asbestos reared its ugly head, had any interest in a job that involved removal, even in the absence of asbestos content.

mrohrmann | 11 years and 4 months ago

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The ISO board will even out the uneven spots beneath it on the old membrane so as long as the new layers are done right no need to remove the old layers unless there are numerous old layers of roof from prior decades left, but if there is only 1 or 2 you should be fine. Otherwise removing it will add significant cost to the job. We looked into this exact issue extensively for a roof on a small commercial building about 6 months ago. Good luck!