1930’s suspended floor. Damp walls.

[Nbarney]

First time poster here.....

I am renovating a 1930’s house with a suspended timber floor. All joists have been renewed and caber floorboards on top. The inside of the void has been tanked.

The question I really want to know is what to do outside. The house is rendered so it sits flush to the pathways. Photos included. There is no damp proof course, and the outside level is higher or at least the same level as the inside suspended.

We noticed last week with all the bad weather that there were a few dark spots on the inside tanking showing through. We know that water will occasionally sit in the void which is a given on occasions of heavy rain.

My question is what to do with the outside around the house to reduce possible damp. Ie. Cut back render etc

 

[Feltwell]

Welcome!

It doesn't sound like your house has been very sympathetically treated -There should be no need to "tank", if that is what has been done, the sub-floor void. If joists have rotted then it's usually a problem with sub-floor ventilation - there should be air bricks in the walls, preferably on opposing walls, to allow a good flow of air underneath the floor. If you haven't got air bricks you should fit some, to stop your new joists having the same problem - if there are some there then make sure they are all clear.

Your house will almost certainly have a DPC - it would be extremely unlikely that a house built as late as 1930 didn't have one. It may well be at the same level as the bottom of your floor joists, that is a common location, it will be made from slate or bitumen most likely.

The outside ground levels really need to be at least 6" below the DPC height - so you may need to cut the pathways back and form a trench, the ground levels should definitely should not be at the same height as the internal floors. The render shouldn't bridge over the DPC, I suggest some gentle exploratory removal of the render to see what lies beneath.

 

[MatthewC]

I absolutely agree with Feltwell. I had all sorts of problems on my house - see my blog in 2010/2011 (hit the "Contact" thingy on the right and click on the circle). My house is older than yours, in limestone with no DPC.

One problem I had was with my suspended floor, where the path was concreted up to the wall and at the same level as the floor inside. The concrete was ensuring that the base of the wall was always wet, made worse by splashback when it rained. The joist running along the wall inside was totally rotted, and all the board ends were gone as well, so I had to sort all those. I also lowered the concrete path and cut it back by about a 10" width and put a bit of gravel in it just as a bottom layer. Overall the level was lowered by 8", and it has been great since.

I would suggest that you do this, and you could also cut back the render for the bottom 3"-6" to allow the wall to breathe more (and so dry out). BTW, what is the wall made of? And the render? (I bet it's cementatious)