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gekkie96 11-13-2012 01:35 PM

Hot Mop - Torchdown - Foam - O My
I have 4,500 sqft of flat roof on my MCM home in southern California. I have multiple quotes to re-roof the house with either a torch-down system, hot mop or foam roof. I'm leaning towards the foam roof and was wondering what others may think is a better roof selection that will last the longest without leaking. Below is a picture of the roof.

Thanks in advance

ddawg16 11-13-2012 02:34 PM

Aaron....I just went through that decision process (minus the foam board option)....

I ended up doing torch mop will crack before the torch down will.

Being the perpetual DIY'r....I farmed out the roof to a professional....the guy I used was some of the best money I have ever spent. He is out of Venice....licensed....and even cleans up afterwards.

Let me know if you want his contact info..... on the 2-story addition link in my signature if you want pics....go to the end of the thread.

shazapple 11-13-2012 05:16 PM

Keep in mind that usually when a system is cheaper it means it requires more frequent maintenance to stay leak free. All 3 are decent systems, but if you are looking for a long lasting solution I would vote for the "torch down" (modbit) roof. Ensure the installer has lots of experience because even a good product can be ruined by poor installation.

AndyWRS 11-13-2012 07:18 PM

+1 on the Modbit

I looked into spray foam for my sisters flat roof in Westlake village, i discovered it was expensive. I think i searched these forums for ideas also, and over at CT. I went with the KISS approach. It may or may not be a better solution, it just wasnt in the budget to do foam so we did modbit. I also did not fully research the spray foam option, i did what her budget dictated.

Thats pretty large, make sure they address any ponding water issues. If its uninsulated you may want to even consider polyiso if your going to reroof, that would be the time to get it done. Being CA and our limited rain fall, homes do not seem to be built very well here.

1985gt 11-14-2012 12:14 PM

First of all take the spray foam estimate and throw it out the window. unless you wish to have someone recoat the roof every 5-7 years.

That leaves you with the torch down or hot mopped.

Both are fine, in my opinion the hot mop is 100% better. If both systems are equal. Hot mop will not "crack" quicker, you can get the same granule surface modbit for the cap sheet.

It boils down to the contractor, have them spec both systems the same, IE ISO, edge metal, layers of roofing. ECT.

JWilliams850 11-14-2012 12:31 PM

hot mopping is a dying art in my opinion. alot of roofers see it obsolete. but a hot mopped roof done right will last just as long or pretty close to any single ply membrane. and hot mopped wont "crack" before torch down will if you put the correct cap sheet or cover it in gravel.

AndyWRS 11-14-2012 02:15 PM

Compare warranties, do both products have similar installation and manfacturer warranties.

I do think they are the same

Grumpy 11-15-2012 08:04 AM

Numerous flat roofing options, and I don't like modified much anymore. After learnign to work with single ply membranes like PVC and EPDM, they are far superior. a properly install built up "hot mopped" roof is a good roof. It is a dyeing art, thanks to insurance companies. But PVC will last as long as a good hot mopped roof and is safer and easier and cleaner to install.

Lots of flat roofing options, no two systems are created equal. Learn more about your flat roofing options:

gekkie96 11-18-2012 04:01 PM

We decided to go the torchdown route, thanks for all the feedback. I will post before and after pictures once the new roof is up.

gekkie96 11-19-2012 01:23 PM

A little snag, need some advice.

We opened up a small section of the roof and it turns out we have 3 old roofs on top of each other.

It breaks down like this:

2x6 Tounge & Grove deck then
1/2 inch of insulation then
Tar & gravel roof then
1 1/12 inch of hard insulation then
Tar & gravel roof then another
Tar & gravel roof

My house has no attic and is basically floor to ceiling windows so insulation is very important... (this is an Eichler home)

I'm not sure if I should remove the top two roofs and leave the insulation and the other old roof and put the new roof on top or remove all 3 roofs and insulation to get to the deck and replace any bad wood and then put in new insulation and the new roof? On one hand I want to remove everything and replace any bad wood and start from scratch but then I worry about the cost and if I can afford to redo all of it. What do you think would be the smartest thing to do?

Here's a picture of the roof open

gwa 11-19-2012 03:56 PM

You should remove everything down to the wood deck. The bottom layer of insulation only has an R-Value of 1.36, so it doesn't add much. Tear it off and mechanically fasten polyiso followed by a cover board. Then you're ready for the APP mod bit roof system.

gekkie96 11-19-2012 04:05 PM

I'm thinking the same GWA. What would a sheet of 2' polyiso cost about?

gwa 11-19-2012 04:11 PM

I'm sure one of the contractors can answer that for you.

AndyWRS 11-19-2012 06:27 PM

Ideally you want to tear off all layers. The polyiso is not cheap, i would think your looking at $29 per sheet just for material.

Does the contract have anything about extra layers or did the estimator just miss it? Polyiso + installation + the possible extra layer charges could really add up. You may actually need to leave a layer of tar and gravel ( meaning tar and very little gravel because all the loose gravel should have been removed prior to roof #2) to avoid having to spend thousands on a complete tear off and new insulation.

If i was going to live there a long time, and i had the $, i would tear it all off and put new insulation and then roof it.

At least the weather is good here atm.

1985gt 11-20-2012 12:03 PM

Tear off and start from bare wood. Nows your change to add tapered ISO to give the roof some slope if needed. Sounds like the "contractor" should have taken a test cut before giving you an estimate. Looks like you got a redo on your hands. I would possibly look at a different contractor. This all should have been done before he gave you an estimate.

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