Some background: There was a repair done to a roof but I'm not entirely sure what type of roof it is nor what kind of repair was done. It looks like there was some rotted trusses but again uncertain.

My questions given the following pictures:

  1. What type of roof is this?
  2. What kind of damage occurred?
  3. How much should I expect a repair like this to cost? (order of magnitude $1-$5k, $10k+, $20k+)
  4. It looks like they did more than just repair the hole. What type of work additionally was done? It looks like some sort of plastic sheeting. Is this standard?
  5. Does the repair look like it was done properly?

This looks like the roof after a sistering of the joist was done?

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I think this is the rotted part where they had to remove parts of the roof.

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  • 1
    I’m voting to close this question because This question does not appear to be about home improvement within the scope defined in the help center.
    – FreeMan
    Jul 28, 2022 at 11:57

3 Answers 3


It looks like a "flat roof with parapets".

It does appear, based on those pictures, that some rafters were repaired. It looks like the original roofing failed, allowing water through. It rotted through the decking and started rotting the rafters as well. The rafters appear to have been sistered and/or replaced, then new decking was applied.

After the decking was repaired, it appears that they put on some sort of a rubber roofing membrane and applied the appropriate coatings to finish the waterproofing seal and to protect it from UV.

How much it cost is totally off-topic because prices vary by locale and day of the week. You'd have to get estimates from local companies to determine what that would have run wherever it is that you live.

  • Thank you this was helpful.
    – Jeff T
    Jul 28, 2022 at 19:21

Pricing is utterly off-topic, since it varies widely by location and over time. So we'll not get into that.

It appears that it was a "hot-mop asphalt roof" (tarred felt strips covered in hot liquid tar, applied with a mop) and it was repaired to be some sort of membrane (EDPM rubber or some other single-sheet roofing, no seams or welded seams) both of which are typical for (nearly-)flat roofs, with the tar being more common on old ones, and the rubber being more common on new ones or re-roofs.

The white color will also reduce heating in summer.

It would have been a good opportunity to apply additional insulation, as there seems to be none at all, but more insulation can also be applied on top of the membrane, rather than under it.


My bet is the roof isn't properly sloped there. Water ponding is a serious problem for flat roofs, and the fact that it's in the middle probably means the decking sagged and created a pond, which eventually penetrated the roofing material and damaged the decking and joists.

The joist looks sistered... but it's weird. Normally you sister across the damaged part. It looks like that new 2x4 stops at some sort of vertical member next to the part that looks damaged. I'd bring in someone (not a roofer) to look at it and make sure the joists look OK and the slope is correct. Then, and only then, would I bring in a roofer to re-roof the area.

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