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Hi

I have a 1920s semi which is built in an area where the houses have a gap under the floorboards and you can see the land below. This land is damp but it is common on our street and it never caused a problem before.

Our house does not have a damp proof course that I am awae of.

The house never suffered from damp but we have decorated with lining paper and also fitted a wooden floor with a membrane (padded stuff) since we installed this the damp has spread from the skirting boards in spots around the dining room usually around the plug sockets and also the chimney breast.

Someone suggested that they had a similar problem with the same type of house and that we would need to go under the floorboards, remove a brick from the wall and remove debris from the cavity as this is what is causing the damp...but would like some 2nd opinions please?

I have 3 year old twins so would prefer not to have to rip up the new wooden floor and install damp proofing/replaster if the above would work or another option.

any help gratefully received.

ideally it would be best to cover the ground under the floor with concrete to keep it clean and well ventilated.
But because you have installed the flooring and dont want to remove it,I would install more airbricks to create more airflow and dry out any moisture that occurs.

Hi

Thanks for the reply. I had looked into the Holland damp proofing system whereby they install a system similar to airbricks around the external part of the property. Have you heard of it and if so do you think that this may be a good alternative?

thanks

I have heard of it but never used it and dont know what the cost is

The "Dutch" airflow system where circular air vents are inserted at approximately 300mm intervals horizontally along the perimeter of the property do not work. In principle, the system was designed to allow a higher rate of evaporation from within the centre of the substrate (in your case solid brickwork)

Please don't be confused by the purpose of this system, the system is designed to combat the effects of rising dampness and not to increase sub-floor ventilation as the vents are only inserted into the centre-3/4 of the wall and not completely through it.
If it's to increase sub floor ventilation, then Welsh Brickie is correct, install air bricks below the internal timber wall plate. I recommend, installing a minimum of 2 9x3" bricks per elevation (side) to reduce the risk of sub floor humidity buildup which can lead to defects such as wet rot, dry rot and insect infestation. Basically you want to achieve 1 air change per hour.

If you want to stop rising dampness, get a new DPC installed, this can be either physical or chemical. This will form a barrier to any rising moisture using capillary action through the brickwork.
The Dutch system relies on moisture evaporating from the masonry before it becomes a problem but the amount of evaporation achieved is minimal and as such has been removed from common practice.

Thanks Refresh PSC, that it great. Thank you

Would you know roughly what I should expect to pay for a Damp Proof course for a 3 bed semi? Our laout is hall, front froom and combined dining kitchen.

Thanks for all your advice so far, its been really appreciated!

You could be looking up to £50 per linear meter for a chemical DPC but this would obviously depend on the company and also the amount of meterage being installed as they may drop the price per meter for larger jobs.
Installing a physical DPC will cost a lot more and the price will depend on the type, thickness and areas needed. That will require a site visit.

A physical is better but chemical should suffice.

I used the Holland Damp Proofing system on my property and it has helped with the damp issues i had, its always worth hooking at the different options available. It seems to have done the job for me but then all properties are different