DIY Home Improvement, Remodeling & Repair Forum

DIY Home Improvement, Remodeling & Repair Forum (
-   Decks & Patios (
-   -   Waterproofing Over Deck Joist (

Scratch3386 08-11-2012 11:32 AM

Waterproofing Over Deck Joist

Earlier this year I hired a highly-rated local company to refurbish my aging second story wooden deck. It's on the large side: 28' x 40'. The project involved replacement wood decking and railing up top, and underdecking below, with the original deck supports and wooden joists left intact.

Unfortunately the decking crew and the underdecking crew were separate -- as it turned out the decking crew were (allegedly) not informed that underdecking was going to be done as well. The redecking was done quickly and well. The underdecking crew, however, had to remove and reinstall the vinyl soffit four times before it finally all fit together correctly and was allegedly watertight.


The big problem is that since the job was completed in early June the underdecking has leaked - persistently - at the double beam that runs parallel to the house right at mid-deck. I want to partially enclose underneath the deck - have already had concrete laid down - and install lighting and outlets there as well. With water leaking, this is obviously not a good idea.

The company owner has had his 'best guy' come out 4 times now attempting to caulk underneath, and also caulk between the deck boards above the beam (unsightly IMO) in an attempt to redirect the rain water away from the joist. These efforts have not fixed the problem. This 'best guy' (who's part of the abovementioned deck crew) has repeatedly told me that had they known the job also involved underdecking, the deck crew would've taken extra steps to waterproof the beam area FROM ABOVE, BEFORE they installed the new deck boards.

I just had the company owner to my house again and he's beginning to mumblemouth me about this has never happened before; they don't actually warranty against leaking joists; etc. I've told him straight up that I consider the fault to be on him and his crew for one hand not knowing what the other was doing. I've relayed to him the comments from his 'best guy' and that's when the mumbling started.


What I want is the deck boards directly over the leaking beam to be pulled up (had they used screws instead of nails it'd be easier), and flashing, soffit, and/or other waterproofing materials installed over the joist FROM ABOVE as needed.

The company owner's opinion is that this won't solve the problem. From my experience many years ago doing roofing, I however believe it will.


nealtw 08-11-2012 12:45 PM

I have never herd of anyone putting soffet under a deck that wasn't covered with a water tight membrane.

oldognewtrick 08-11-2012 05:07 PM

I'd really like to see pics if you can post them.

Oh, yeah :welcome: to House Repair Talk!

Scratch3386 08-12-2012 09:45 AM


Originally Posted by oldog/newtrick (Post 76021)
I'd really like to see pics if you can post them.

Oh, yeah :welcome: to House Repair Talk!

Thanks for the welcome. Here are photos, as requested.

The deck from above:

The caulking attempts on the surface deck boards:

The underdecking, with gutters & downspouts:

Scratch3386 08-12-2012 09:46 AM

And the problematic center joist (beam, actually):

Scratch3386 08-13-2012 01:28 PM

*TEST* My subsequent posts appear to be held up in Moderation.

(Edit: ah, there they are)

Scratch3386 08-13-2012 01:31 PM


nealtw 08-13-2012 05:28 PM

I know you came for answers but i think you're going to get more questions.
What is supposed to stop the water from entering the deck? How does the water get out from between the boards? Why would you not use vented soffet?

oldognewtrick 08-13-2012 06:06 PM

Neal, the third pic in the first set shows a gutter running along the beam. I think the soffit is suppose to dump water into the gutter. I'm baffled as to why they used vinyl soffit material and didn't instead use something like bi-rib metal roofing panels?

nealtw 08-13-2012 07:20 PM

It's interesting and new to me, and how do you clean the gutters?

All times are GMT -6. The time now is 05:20 PM.