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pwalker

01:52PM | 10/10/03
Member Since: 10/09/03
2 lifetime posts
Bvroofing
I'm having a 40 year old tar and gravel roof replaced with 3 tab shingles. For some reason the gravel is not scraping off. The roofer wants to replace all the boards underneath. Is there any other alternative?

pgriz

05:31PM | 10/11/03
Member Since: 01/21/03
66 lifetime posts
RED FLAG!
If your tar and gravel roof is sloped 2:12 or less, you should NOT be replacing your roof with 3-tab shingles!!! Use any of the products designed for low slopes, ie, elastomeric membrane, low-slope metal roofing, or even, (gasp) tar and gravel. 3-tab shingle are not desiged to be used on low-slope roofs. In every situation where we saw tar-and-gravel roofs replaced by shingles, even the so-called "low-slope" shingles, the homeowners were experiencing persistent and extensive leakage. I guess you can figure out my opinion of the roofer that proposed this solution to you. So my first bit of advice is to get another roofer, and then see what this new party suggests.

pwalker

08:27AM | 10/15/03
Member Since: 10/09/03
2 lifetime posts
Thank you for your reply.

The slope is 2.5:12. Three roofers came out and each of them said that shingles would be a viable option. The roofer we selected then couldn't get to bare wood so he ended up replacing the plywood. He said the inspector said they had to follow the manufacturers recommendation. But if you can go over one layer of shingles with another layer, why can't you go over a layer of tar with shingles?

pgriz

09:31AM | 10/15/03
Member Since: 01/21/03
66 lifetime posts
Shingles are designed to shed water. The tar strips at the edges are there to prevent the wind from lifting the edges and breaking off the shingles. This tar strip does not, however, create a waterproof surface. Therefore if there is possibility of water backup, the water can move up between the shingles and cause leakage through backup. For that reason, especially near the eaves, it is common and required to install eave protection in form of ice-and-water shield membrane or equivalent, in areas where there is snow and/or freezing conditions. I've checked the specs on most shingles and they all say 3:12 or better. Since it does snow in Seattle, I'm still leery of the solution your roofers are proposing (unless they put ice-and-water shield under the shingles).

The reason you can go over an existing layer of asphalt shingles is that they are supposed to be flat, and the second layer can lie flat upon the first. If the surface is not flat, then the shingles will not lie flat against each other and the tar strip at the edge will not properly seal. Later a strong wind can lift the unsecured edge and tear it off. Going over an uneven tar surface will not allow the shingles to seal properly due to the unevenness.

From your last post, it seems you've gone ahead and had the roofer do it the way they suggested. I hope you have done your homework and picked a roofer who has been around for a while, since I think you will be calling him again rather soon. Then again, maybe you'll be the first who is satisfied with the results. In my area, I've got two neighbours who switched from tar-and-gravel to asphalt shingles (supposedly low-slope), put up with them for about five years each, and one has gone back to tar-and-gravel, and the other went to torch-on membrane. So good luck.

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