Damp under wooden floor.

[djheath]

Hi, I live in a house built in 1911. I moved in just over a year ago and the previous owners had carpeted the downstairs living room and dining room with pretty hideous old carpet! I was thinking to go back to the original floor boards which look to be in relatively good condition. I've taken up one or two of the boards and found a lot of damp and salt deposits in the soil under the floor boards. Our surveyor said there was no over site when we bought the house and may have damp problems. Below are some pictures I took of the damp and the state of the boards. Is this damp something to worry about if we remove the carpet and then sand and renovate the boards? I.e will we start to experience smells more or would filling the boards help with this? Also can anyone tell me what the boards are made from? I expect they are pine but want to make sure.

For info: The soil is ten inches from the bottom of the boards. They are laid on 4 x 2 joists which are themselves laid on 4 x 2 joists which are laid on brick walls which touch the soil. None of the wood is wet, but the bricks are damp to touche, although that could just be the salt deposits.
Current board condition:

Under the boards: Tissue was being used to plug a gap in one board!

Ideally I would like to lift all the boards, lay a proper concrete over site and relay the floor but time and money wont allow this.

Any advice would be great.

 

[JohnD]

any sign of slate in the mortar beds in the wall or under the bottom joists?


how many airbricks are there, and how clear are they? Can you feel air blowing through them?

 

[djheath]

No there is no sign of slate. The whole building has no damp proof course, but the previous owners had a injection dpc added to the exterior walls about 15 years ago. The air bricks a clear, although there is only one at the rear of the property (where the photos were taken) and two at the front. Sticking my head under the floorboards I can see the air bricks and see they are clear. There is also holes in the brick walls supporting the joists to let the air flow through.

 

[djheath]

Right ive had a dig around some more. The "soil" doesn't really seem to be soil actually. I have poked it with a scredriver and it is very hard and chips off into bits. It has lots of stones in and is very sandy. Seems almost to be very compacted hardcore rather than a concrete slab or soil. Does this alter anything?

I've checked all air vents - two small ones at the front of the house, one large at the rear and three large down the side of the house - all are clear.

Can I lay a damp proof sheet across the bottom of the "soil" as a dpm, making sure to not cover any air holes? Should it go up the sides of the walls at all?

I'm not really sure what I am trying to stop though or if this is problem I should worry about as nothing seems rotten in any of the wood.

Thanks for any help.

 

[JohnD]

I bet it is poor-quality concrete. I've had that in an old house. It will tend to be damp as it is not very dense. In my old house I considered laying a thin slab of concrete over the top, either with a moisture-proof additive, or with poly dpm under it.

However damp will still come out through the brick sleeper walls for a course or so, and my house was not very wet, so I didn't

Adding a few more airbricks and getting a good airflow will keep the subfloor humidity down. Verify that there is no source of damp such as a leak from a water pipe or drain (including radiator pipes). This will be easier if you have a water meter as the bubble may never stop spining.

 

[dann09]

1. Are your walls solid or cavity?

2. A 1911 house in a town almost certainly has a DPC - back then, bitumen was a DPC material - what look like bitumen snots can be seen in pic 3. Investigate harder for a DPC.

3. Air bricks can be cleaned by blowing thro from the outside. As john asked - how many and where located?

4. The sub soil can be covered by sheets of overlapped poly - lap the sheets up the walls 150mm. Doing it would be taxing.

5. Check, as best you can, the state of the joist tails resting in pockets in the external walls. All joists touching masonry must sit on a DPC.

6. Learn to lift floor boards correctly, dont break them off.

All the above and much more can be researched on the building forum. If you care to, follow my posts on similar subjects and issues.

 

[djheath]

1. Are your walls solid or cavity?

2. A 1911 house in a town almost certainly has a DPC - back then, bitumen was a DPC material - what look like bitumen snots can be seen in pic 3. Investigate harder for a DPC.

3. Air bricks can be cleaned by blowing thro from the outside. As john asked - how many and where located?

4. The sub soil can be covered by sheets of overlapped poly - lap the sheets up the walls 150mm. Doing it would be taxing.

5. Check, as best you can, the state of the joist tails resting in pockets in the external walls. All joists touching masonry must sit on a DPC.

6. Learn to lift floor boards correctly, dont break them off.

All the above and much more can be researched on the building forum. If you care to, follow my posts on similar subjects and issues.

Thanks for your advice.

Firstly the property doesn't have a dpc between bricks. There is a tar paint on the bottom edge of the exterior of the building but it is thin black paint rather than a proper course. The surveyor confirmed that there is no dpc in the building. The bitumen snot is actually a shadow from a cobweb which shows up from my crappy camera phone pic!

My wife and I have decided to rip up all the boards this coming weekend and fit insulation, so I can investigate the ends of the joists and lay a dpm sheet over the sub soil, before replacing and sanding the floor.

As said above there are 6 air bricks around the building which are all clear. When the floor is up I will check they are not covered at all and cleaned from the inside.

Finally that board in the photo was already broken, hence why I lifted it up. It will be replaced this weekend!

Thanks again for your help.

 

[dann09]

Its your house, your money and time, but the odds are very high that there is a DPC down there.
Dont simply rely on a surveyors report that was made as she or he rushed thro the property.
I doubt that they probe mortar beds with screwdriver tips, or dig down a little to recover the original clearance. In my limited experience, I've never seen them do that. Maybe thats just me?

Take great care in carefully lifting the boards - there's advice on how to do it on here or the building forum. Check the price for new T&G. It might pay you to hire a joiner for a couple of days.

 

[tony1851]

If you put any damp-proof membrane over the 'soil' with the intention of stopping any damp from the ground rising, you risk forcing additional moisture up the small sleeper walls. If these have no dpc under the timber, you will make the situation worse and actively encourage dry rot.
IMO best advice is to add 1 or 2 extra air bricks to ensure good ventilation, which will quickly remove any moisture.
Your situation doesn't seem too bad at the moment - don't spoil it.