Advice on deck repair

gabchoud · 09-10-2009, 10:38 AM

I have a deck repair that I need some ideas on. The floor joists appear to be cantilevered into the brick work of the house. At least I can tell you that there is no band joist against the house.

In any case the original builder sealed the joists to the building with roof tar. There are two problems with this. Problem one, the tar cracked and seems to be letting rain water into the wall cavity. Problem two is that it just looks like crap.

So the question is, how to make a repair that will be long lasting, and look a little better?

The owners idea is to chip away the tar, and fill the cavities with spray foam. I think this would only be a short term fix. As the deck moves due to moisture and humidity changes the foam would lose it's seal (true?). Plus it would also look awful.

My only thought for a more permanent fix is to flash it out somehow. The deck boards are 2x6'es so I have an inch and a half to secure something to the house. The problem with this fix is that I feel the flashing would need to "float" beneath the deck board to allow for deck movement. So, how do I secure the deck board back after flashing?

Help me out folks.

Bob Mariani · 09-10-2009, 09:20 PM

spray foam would serve no purpose here. Flashing would need to be configured to shed water away from the joists and be cut into the brick and sealed with mortar or caulking above the joists. The joists would not be attached to the flashing. Use a polyurethane caulk to seal the space around the joists where they enter the brick. If the space is large, fill with the correct size foam backer rod first. A mason supply house will have this stuff. It is not the same as spray foam, more like a foam rope.

Just Bill · 09-11-2009, 08:00 AM

I have seen small decks built this way, with standard framing lumber cantilevered through the side of the house. Since this is standard lumber, it will not last long outside in the weather, my guess is <10 yrs. It should be preassure treated wood. The other problem you already understand, sealing the hole is not simple, and it will have to be redone periodically. What Bob suggested.

gabchoud · 09-11-2009, 02:20 PM

Thanks Bob, that makes sense. My only other thought was to use a rubber roof type membrane, and secure it to the brick face similar to the way I used to do when erecting exterior walk-in coolers. If I install it right I can provide a slight droop between each of the joists to allow the water to run away from the house. I would still want to seal the cavities around each of the joist where the enter the brick veneer.

Bill, fortunately for the homeowner the deck is constructed from PT boards, so rot is not yet an issue. This is one funky deck. I can't say I've ever seen one installed like this before. I don't know if it is truly cantilevered, (secured to the interior joists) or if it was installed during original construction before the brick veneer was completed. Suffice it to say that I would never build one like this myself.

Let me know what you guys think of the rubber roof idea. I will be talking with the owner tonight.

Tom Struble · 09-11-2009, 03:48 PM

if there are no post it must be cantilevered
build a roof over the deck ,only way to be sure with those kinds of details

oldfrt · 09-11-2009, 05:11 PM

Quote:

Originally Posted by Bob Mariani

spray foam would serve no purpose here. Flashing would need to be configured to shed water away from the joists and be cut into the brick and sealed with mortar or caulking above the joists. The joists would not be attached to the flashing. Use a polyurethane caulk to seal the space around the joists where they enter the brick. If the space is large, fill with the correct size foam backer rod first. A mason supply house will have this stuff. It is not the same as spray foam, more like a foam rope.

Best advice here.
If you can get a piece of flashing bent into a Z shape it could be notched into the top of the joist 1/4",just enough to to keep water from running back on top of joists.

Tom Struble · 09-11-2009, 06:24 PM

thing with the cantilever joist is you can get alot of water following the joist
back into the house from the bottom
relying on caulk as the primary moisture barrier well....

Bob Mariani · 09-12-2009, 09:22 AM

use window flashing tape in instead of the roofing membrane. It will be easier to handle and a bit sticker. Pressure Treated wood resists rot, this does not mean it will never rot. the protection wears off. If in contact with a cement product, other wood, wrong nails or earth it's life span is decreased.

**Gary in WA** · 09-12-2009, 02:13 PM

Measure and install solid blocking between joists, with front face flush with exterior of brick. Install flat flashing between joists on the blocks and extending down over the tops at lower bricks below hole. Seal with window tape to joists, not brick. Install L-flashing with 1/4" lip to joists only, caulk joint underneath where both meet, and on joist where flash contacts it. Install cap flash in mortar joints of brick, overlapping L-flashing. Don't nail inside of deck board at brick side to rupture flashing. L-flash and cap would float by with deck movement, each secured to different things.

At circle detail, where cap flash would be into brick grout and decking would be shingles: http://www.buildingscience.com/docum...ils/#Figure_02
Be safe, Gary