Damp wall and rotten joists

graeme16

Purchased a 3 bed semi last week and have found some rather significant damp problems on the ground floor. There is what appears to be damp 'rising' up the external / internal wall between the lounge / kitchen and the floors where springy. I have pulled up two floorboards to find the ends of all the joists as they sit in the sockets to be rotten. it's obvious that I will need to replace the joists however I'm interested in peoples opinions on what the potential causes are. I am in touch with some damp 'specialist's' int he interim. I cannot see an obvious DPC and I believe the house was built in the 1930's. Air bricks are all clear and the decking at the back of the house was stood off the wall. I have noticed the ground level is at the same height, if not a little higher than the internal floor area and as I have pulled the gravel back, the bricks behind are obviously wet. Seems as though this is the likely culprit? I plan to pull all the gravel away from the house this morning and maybe understand more about where the current DPC is. Would this mean the cavity has to be bridged if the damp is soaking into the internal walls?

stuart45

The cavities could be blocked up above the DPC. You have to remove a few bricks.

FreeBear

In image No.3, you have a row of obviously damp bricks, yet the ones just above appear to be bone dry. This suggests that you have a DPC and it is doing its job. Ideally, the ground level should be ~150mm blow the DPC, but on a 1930s house, that may well expose the footings. 75mm below the DPC and some gravel would be a reasonable compromise.

If (when) these damp "specialists" return, do not be suckered in to spending money on injected chemical DPCs or the waterproof render/plaster treatments they usually recommend - Neither are effective long term cures (they just mask the problem for a few years). And if they recommend the schrijver system, give the guy a kick up the backside as he leaves.

tonyh66

looks like the joists are sitting on top of the damp course level, when you replace them make sure there there is some there to stop bridging. Also look to lower the ground level a bit. Finally that drain looks close to the damp area, make sure its not its not leaking in against the wall

graeme16

Appreciate the responses. I have moved all the gravel away and think the ground is just way to high. I'll probably remove some more and wait whilst the bricks dry out. Hopefully understand more where the DPC is then however it makes sense on the location stated above. 

stuart45

Building regs allow 2 courses of engineering bricks in a strong mortar as a DPC, so you can't always find a normal one in the joints. It would normally be under the door frame.

Bendy_House

Doesn't the presence of the air vent immediately under the door cill suggest the DPC is just above this? In which case, the level the gravel was at wasn't  really too excessive - ie, the gravel and ground wasn't actually BREACHING the DPC, but just not at the min recommended level below it, 150mm.

Graeme, I suspect - but obviously don't know - that there's summat else amiss. Damp is either rising up past where the DPC should be (IE the DPC is damaged), or is coming through from outside, which would suggest that perhaps the cavity is breached by debris or something, or there is a particularly bad source of water there, a drain or pipe, something like that.

Now you have the boards up, it should be possible to investigate. Is this something you hope to fix yourself, or are you going to get someone in?
For the former, I think what I would do is expose the damaged joists back to a stage where there is zero rot, and then the recommended amount past this (look it up!). Then build a temp support for the joists - a stack of bricks or similar - and cut off all the affected ends. Once you've pulled these ends out from the supporting cavity wall, it should hopefully become clear where the damp is coming from - either from below, or from outside.

theoretica

You also have the drains there - worth checking that out and that the water is going down them and away. 

FreeBear

Bendy_House said: Doesn't the presence of the air vent immediately under the door cill suggest the DPC is just above this? In which case, the level the gravel was at wasn't  really too excessive - ie, the gravel and ground wasn't actually BREACHING the DPC, but just not at the min recommended level below it, 150mm.

If you look at the bricks that are obviously damp and covered in algae, they are two courses down from the bottom of the door - The air brick (I suspect) is sitting on the DPC.

Sometimes the DPC is above an air brick, sometimes below. There are no hard and fast rules as to where it might be thanks in part to evolving building standards.

stuart45

A good starting point when looking for a DPC is directly under the door frame. A standard method of construction is the engineer etc to set timber pegs in the corners at DPC level. The brickwork is then built up close to this level, then the bricklayer uses his club hammer to fine tune the peg to his corner.
The door frames were then set on top of the laid out DPC ideally all the heads at the same level.

graeme16

Appreciate all the information. I have a builder friend coming around today so hopefully can shed some light the DPC height. I will try and sketch the layers out.