Patio join to house, and damp

[lfnfan]

Hi All

Looking for some guidance on to make sure the drainage setup for edge of patio joining to house is as good as it can be. Getting a bit of a damp smell in one room which suspect might be down to the way the patio meets the house.

I've done a sketch of the current construction. My plan is to dig out the existing sand/ cement/ small rubble mix in the 100mm by the house down to the depth of the bottom of the mortar skirting on the exterior wall, and fill with gravel. The red box on the diagram basically.

I could also put in a damp-proof membrane down the side of the house if that's thought to be a good idea too.

Very many thanks in advance

 

[Mr Chibs]

Really your ground level is too high for the DPC, ideally it should be two courses below, so any splash back when raining etc won’t get above the damp course.

Trench idea is a good start, 150mm better and make the pebbles large, not the 20mm gubbins from Wickes, as this will settle and become solid, again.

I’d put weed membrane down first, then straight with the pebbles, not sand/cement in the bottom of the trench.

 

[lfnfan]

Thanks Mr Chibs

What size pebbles would you go for?

Do you think it's worth putting a dpm along the length of the house-side of the trench?

Many thanks again!

 

[Mr Chibs]

I wouldn’t bother with any dpm.

You want large Pebbles (large as possible) like you get on beaches. That way air can circulate and there won’t be much contact with your wall, so no transferring of damp.

 

[lfnfan]

Great. Massively helpful - thank you!

 

[Halitosis]

I have a similar arrangement but leave the trench empty - that way there definitely won't be any splash up the wall, and also I can see at a glance that no crud has accumulated down there. No damp issues at all and the gap isn't noticeable to us or guests.

 

[lfnfan]

Thanks Halitosis
Have my eye on some nice pebbles so think I'll go the 'filling' route. But I'll definitely be keeping an eye in future to make sure the trench is not filling up with crud.

On the crud point, I'm thinking of putting a concrete skim on the vertical patio side of the trench to help make sure the sub-base doesn't wash out into the trench. The weed barrier will also help. Happy days.