Moisture Where Deck Connects to House

[Andrew Robertson]

I am planning on installing ¾” hardwood floors in my single level home with basement. The hardwoods will be installed above the basement level. As part of my preparations I have been taking moisture readings. The moisture content of the 1/2" plywood subfloor is mostly 8%. However along a certain exterior wall I have had readings much higher 13-18%. The partcleboard I removed along these exterior walls was not wet. Just outside this specific wall a deck ties into the house. Please see the attached sketch.

Note the floor joist run continuously from inside the basement to outside underneath the deck. The exterior edge of the subfloor is exposed to the outside.

What would you do reduce the moisture seen inside the house?

 

[noseall]

Seems an odd arrangement that the joists are continuous from inside to out. How do you counter cold bridging and condensation issues? Why was it designed/built this way?

 

[ree]

Typically, you should have 3/4" ply sub-floor with a 3/8" particle board underlayment - the particle board should stop at the interior side of the sole plate, it doesn't run under the wall studding. The edge of the 3/4" ply sub-floor goes under the wall, and in your case appears to be exposed.

OP, cantilevering joists out to form a deck or balcony floor is common enough but the joists are often very slightly sloped once past the building line ie. the face of the building. This is to shed water away from the wall.

You dont show any flashing - there should be extensively detailed flashing at the wall deck junction, and along the top edges of the joists. Exterior Ply sheathing should typically run down the studding past the decking to finish just below the mud cill - the Masonite siding is presumably fixed to sheathing?. The sheathing should blind the subfloor edge.

FWIW: based on what you describe, and given the recent Berkeley balcony/deck collapse, and other deck incidents, it would be worth your while to have a deck inspection - no way should moisture be creeping into the house interior.

 

[Andrew Robertson]

Please see attached pictures.

 

[ree]

OP, i'm afraid that you must get a qualified inspector on site - eg. such as a Home Inspector, or a Building Inspector or a NACHI Deck Inspector.