Garage threshold rot

[Pattycakes]

Hello- just moved into new house a few months back which has an awesome detached garage i am in the process of finishing main level. The driveway comes right up to the main level garage door and I found the plywood floor and subfloor completely rotted out under the threshold plates. The joists and and other structural wood underneath look ok, obviously ground contact. Curious if anyone has any suggestions based on the pictures as to how to address other than replacing the plywood and subfloor with ground contact plywood and then covering with ice & water shield?

 

[SALIV8]

I have never seen a garage floor setup like that, with wooden joists and plywood subfloor. I don’t even see joist hangers. Do you drive over that?

I wouldn’t think the joists running parallel to parked vehicles would support that weight with plywood flooring.

but yeah I’d rip out all the damage and replace with same material, then waterproof with liquid applied membrane and probably tile it myself. ice and water shield is a good idea too. Can you change the pitch outside the door to shed water away?

 

[Pattycakes]

The asphalt does about a 6 inch rise up to the threshold plate, I think the problem is that the outside edge of that plate is exposed entirely and water can collect at that seam. Not much I can do about the grade. The rotted plywood and osb subfloor was not pressure treated.

and yes this was designed to support an suv or pickup… the structure was built into a hill and there is a lower level with old horse stalls and a 2nd garage door that opens up to the rear. There are multiple 4x4 and 6x6 columns below under the parking section and much of the framing is doubled up and reinforced.
I agree though and don’t love the idea of parking in here regularly so I only pull my wife’s keep in for snow storms (we are outside of Boston)
I will be putting down vinyl plank eventually once the rotted floor and old grease spots are taken care of.

 

[Jeff Ivers]

It is really hard to tell from the pics, but it appears that the asphalt might be slightly higher than the inset area of the door, making that area into a pond from the water hitting the door and running down into that area. I would examine that area very carefully and try to change it so there is a 5 degree slope from the garage door face to the drive and on out away from the building.

 

[Pattycakes]

Hmm what if I shimmed the interior of the threshold plate so that it is slanted towards the driveway to help run the water off?

 

[Hank11]

Pictures of the inside from the lower level might be helpful.

 

[Bert_]

That exposed lip of garage floor absolutely must be sloped to allow drainage. I like not less than a 10* slope.

Depending on how you detail where it meets the walls on either side of the door you may still have some issues there. Hopefully there is some sort of flashing between the wood and the asphalt also. Asphalt looks like it's almost the same level as the garage floor which is a problem

 

[SALIV8]

That last pic looks like you can remove the top inch or so of the asphalt and at least be lower than the threshold on that right side where the puddling is. I’d be sure the asphalt is significantly lower than the garage floor from left to right to account for heave.

Put a level across the threshold also and see what you got. Hopefully you have the pitch and that asphalt height is the problem.

in the meantime maybe a canopy would help, or a trench drain across the driveway.

 

[kaymccampbell]

That plywood looks like it's outside the door. If that's the case, then I'd cut the joists back behind the door, put in a new rim joist, cover it with rubber, zip tape, something waterproof, and pour a concrete sill.

 

[Showkey]

Just a guess……..that detached garage might have been built as shed for equipment like mowers and or work shop.

Plywood and joists can be built to hold full size vehicles…….but……..rarely a good or first choice.

I had “shed“do the same thing with OSB floor, no surprised. Replaced with pressure treated plywood 20 years no issues. The plywood was the threshold and was outside the door and mated to the ramp.

 

[Pattycakes]

Yea it’s definitely not used regularly for the vehicle, but was built to do so back in 2013. I got a few more pics and order PT plywood this morning which I will double up since the original flooring is a 3/4 particle bboard sub floor and then 3/4 plywood. The framing looks pretty good and pressure treated, particle board was just sponging up any water