High damp readings in internal walls

sgjfrods

I have recently bought a house and when doing so the survey flagged up high moisture readings within several downstairs walls. The suggested works required was to take the skirting board off and inject a new DPC. At the time i could see no visible signs of damp and the house was vacant and cold, for these reasons i came to the conclusion that it was nothing too serious and went ahead with the sale.

The house is approximately 1900-1920's build cavity wall construction and has a suspended floor with what looks to be a bitumen DPC.
I have now lived in the house for 2 years and have seen no visible signs of damp, however, when looking underneath the suspended floor found that the floor joists that where spanning onto the wall are visibly damp at there ends. The bitumen DPC is at the same level as the bottom of the joists. (i.e. the joists are sat directly on top of the DPC).Underneath the floor seems well ventilated. I have two main questions:

1.) Does this seem "normal" for a house of this age?
2.) It seems like new DPC's would be injected at skirting board level, i can see why this would prevent damp rising up the walls, however, it would still mean that the timber floor joists would be sat on a wet wall. How is this usually prevented?

Many Thanks for your replies in advance!

stuart45

There may be debris in the cavity that will allow moisture into the joist ends if they are built into the wall rather than sat on a sleeper wall next the inner skin.

sgjfrods

The joists are built into the wall.

Doozergirl

Don't inject a DPC, you just need to find the cause and treat it. The joists should sit on their own damp proof bearing but something's getting to them. Check they're stiing on slate or bitumen themselves, perhaps too.

Investigate and then deal with the rot, if necessary.

FreeBear

stuart45 wrote: »

There may be debris in the cavity that will allow moisture into the joist ends if they are built into the wall rather than sat on a sleeper wall next the inner skin.

At the turn of the century, solid walls were still the norm. Cavity wall construction didn't become widespread until much later - That said, some Victorian properties did have cavity walls, but these tend to be a rarity.


As for the joists, at one time, building regulations did specify that joists inserted in to a wall should be dipped in bitumen - Regs varied from area to area and there was nothing like the national standards that we have today.


For the OP, injecting chemicals in to the wall will do little to prevent damp penetrating the timbers. Save your money and instead, spend it on constructing sleeper walls and replacing the rotten joists.

stuart45

FreeBear wrote: »

At the turn of the century, solid walls were still the norm. Cavity wall construction didn't become widespread until much later - That said, some Victorian properties did have cavity walls, .

The OP said he has cavity walls.

bertiewhite

Do you want people to answer this thread....




or this one?
https://forums.moneysavingexpert.com/discussion/5967845/high-damp-readings-in-internal-walls

sgjfrods

Many Thanks for the helpful responses. Reply to this one please, i started one thread and then realised it was under the wrong heading. I don't know a way of deleting the other thread.

From inspection of the void below the suspended floor, the ground is well below the joists and therefore the damp proof course. From what i can gather from peoples replies floor joists will often run into walls within their "damp zones", but they usually should have their own protection from the wall. I cannot see anything obvious below or around the joists as they run into the wall, however, it seems like they are sat directly on top of the DPC, so in that case am i right in thinking the DPC is acting as the joist protection as well?

I have an image of the problem but i cannot find a way of uploading it on here , it requests a "URL"

Would the initial survey flagging up high moisture readings within the walls be anything to worry about in a house of this age? There is no visible evidence of damp in the walls.

Many Thanks again.

stuart45

From my experience working on old cavity walls the debris in the cavity is sometimes over the top of the DPC. This can be mortar dropping from the build, or from later work. The outer skin allows moisture through in heavy driving rain which runs down the inner face of the outer skin and down below DPC, but if this is bridged then moisture could get to the joists.
On older houses the fill in the cavity was 150mm below DPC but nowadays it has been increased to 225mm because of this problem.

Mistral001

stuart45 wrote: »

From my experience working on old cavity walls the debris in the cavity is sometimes over the top of the DPC. This can be mortar dropping from the build, or from later work. The outer skin allows moisture through in heavy driving rain which runs down the inner face of the outer skin and down below DPC, but if this is bridged then moisture could get to the joists.
On older houses the fill in the cavity was 150mm below DPC but nowadays it has been increased to 225mm because of this problem.

Stuart is on the right track here in my view.

I would try to inspect the cavity. This is easier than you might think as endoscope cameras connected to a laptop are inexpensive these days and an inspection can be carried out by simply drilling holes in the wall at regular intervals and inserting the endoscope to have a look at the cavity. That or cut holes in the wall just above joist level and use a small mirror on the end of a stick to look down the cavity.

sgjfrods

Thank you. I think the camera idea seems like the less destructive option. I will take a look and see.
One point to note though the wall where the damp joists run into isn't an external wall. It used to be the back wall of the house but an extension got added and therefore its now an internal wall.
I suppose damp can rise through the filled cavity and up into the joists from there though, it doesn't have to come from driving rain?
Also lets say the cavity is full of debris above the DPC, how on earth do you clear it along the length of the wall?