Damp beneath living room floor

[homeowner123]

Hello,

I've recently been having my 1920s end-of-terrace house renovated, including replacing the floorboards in the living room on the ground floor.

When the old floorboards had been taken up, however, I noticed a patch of damp running along the inside of the external wall under the floor.

I've also noticed on the other side (the street side) that there are gaps between the paving and the wall and I was wondering whether these also might be allowing rainwater to enter, possibly causing or exacerbating the problem.

In addition there is a noticeable and unpleasant musty/damp smell.

I have had two companies come over to inspect the damp and both have suggested installing airbricks along the affected wall as well as various other solutions including an extensive chemical DPC.

I'm wondering therefore what the best way to proceed would be? There is an airbrick at the front and back of room but none along the external wall (where the damp is). There aren't any signs of damp on the plastered wall above the floorboards, nor did the handheld damp meter used by one of the surveyors detect anything, however I am somewhat concerned that it may become a problem in the future.

I have included photos of the damp patch on the inside and the paving gaps on the other side of the wall.

Thanks in advance

 

[JohnD]

All the joists look strangely new so I will guess there has been long-term damp.

There are pipes containing water near the damp patch so start by searching for a leak.

Work out where the incoming water supply pipe is. Most likely it runs in a straight line between the stopcock or water meter next to where the front gate used to be, and the stopcock beside where the kitchen sink used to be.

If the subfloor void is not well-ventilated with multiple airbricks on at least two sides of the house providing a through draught, get them installed.

Take some more pictures of the other side of those walls. Include particularly any manhole covers, soil pipes, downpipes and gullies, and any signs that concrete or paving has been repaired or is sloping towards the house causing puddles to lie against the walls.

Most likely the original drains and gullies were glazed clay and have been broken at the traps and bends for about 75 years, so probably leaking.

A chemical treatment is 100% useless. It will not repair broken drains or leaky pipes or rainwater gaps. It will however put money into the pocket of the person who sells it to you.

 

[homeowner123]

Thanks for the quick reply JohnD

There are pipes containing water near the damp patch so start by searching for a leak.

A plumber has inspected the pipes in the photos recently and didn't see any leaks however I'll double check.

Work out where the incoming water supply pipe is. Most likely it runs in a straight line between the stopcock or water meter next to where the front gate used to be, and the stopcock beside where the kitchen sink used to be.

Yes that's right, the mains water supply comes in under the front door on the other side of the room and leads to the kitchen.

Take some more pictures of the other side of those walls. Include particularly any manhole covers, soil pipes, downpipes and gullies, and any signs that concrete or paving has been repaired or is sloping towards the house causing puddles to lie against the walls.

There's no manhole on the street side however there is a square patch of concrete which looks different to its surroundings. It is on the opposite (right-hand side) of the corner of the room in the photo.

I'm not sure if the paving is sloping towards the house but the gaps do seem to take a long time to dry after it rains.

Do you think the damp patch is more likely to be rising damp or a leaking pipe/water ingress somewhere?

Thanks

 

[JohnD]

unlikely to be rising damp

more likely a leaking drain, pipe or gutter.

Go out after rain and see if water is falling against the wall from the gutters, or if the downpipe is blocked.

 

[bobasd]

that floor carcassing is well wrong an looks like the work of DIY'ers or Damp an Timber people.
the external render is touching the ground - there should be a small gap to prevent capillary action an a Bell Cast to throw off water.
is thhe walls solid?

that external patch you show could have been a recess for an air brick - maybe the ground/pavement has been raised over the years?

install 9" x 6" plastic air bricks every 1500mm or so.

all floor joists an supportin plates should be protected with DPC material from masonry or ground contact.

to keep them firm joists tails typicly sit in hacked out brickwork pockets.otherwise the floor could move.

 

[homeowner123]

Hi bobasd,

is thhe walls solid?

Yes, according to the building survey, they are.

there should be a small gap to prevent capillary action an a Bell Cast to throw off water.

Do you think the damp is rising damp or is more likely to caused by the rendering or something else?

 

[blup]

Does the house have a damp proof course, either original, like slate, or added later, such as a chemical dpc.

If so, does the damp area appear below this?

Blup

 

[foxhole]

Does look like external level has been raised compromising air brick which has now become a drain to the under floor area causing your damp .

 

[bobasd]

youve probly got the original DPC in that wall but it might have been bridged by the render or sunk below any higher ground level.
i cant see any signs of modern injection holes inside or outside.

with the info youve given i'd say it was ground water in that corner.
any water/moisture comin up from the ground or upthe walls is rising damp.
water comin through a wall is penetratin damp.

i'm surprised that no risin damp has been found in the walls - esp given the render in ground contact with a solid wall?

 

[homeowner123]

Thanks bobasd,

youve probly got the original DPC in that wall but it might have been bridged by the render or sunk below any higher ground level.

Does the bottom of the wall actually need to be rendered like that? Would it be ok to just remove the rendering and leave the brickwork exposed?

with the info youve given i'd say it was ground water in that corner.
any water/moisture comin up from the ground or upthe walls is rising damp.

water comin through a wall is penetratin damp.

Right, I see the distinction. So the damp in the corner is more likely due to moisture in the earth under the house than rain water coming in from outside?

I've included another photo of the render in case it helps.

 

[blup]

Could you show on one of the pics where the bottom of the external wall is in relation to the inside wall? That will help identify the extent of the bridging.

The bellcast is allowing rain to drip clear of the brickwork so removing it will create, not remove, a problem.

Blup

 

[bobasd]

thers no BellCast ther?

OP, what youve got is a rendered plinth not a full gable renderin.
Plinths dont usly have Bellcasts.
the plinth was probly instaled in an attempt to prevent dampness - the pointing looks pretty new as well.
hack the plinth off the wall, an clean an point the lowerbrick courses.
look for a DPC while you do it.
is that a private pathway or the street pavement? that gables wher you needa few air bricks.
istill dont now forsure wher the water is comin from

 

[JohnD]

I'm still open to the idea of a dropping gutter or drainage fault.

We haven't seen a wide angle, standing-back pic of the side of the house yet.

I don't know about council pavements, but on private land I'd want to cut the asphalt back and dig a trench at least a few inches wide beside the house, add airbricks, look for damaged drains, remedy any pointing or other defects, backfill with pebbles to allow free draining and prevent damp movement by capillarity.

Plinths are often intended to remedy damp but they usually have the opposite effect by preventing evaporation from the brickwork.

 

[Nige F]

While the floor is up it would be good to add foam lagging over that old hair felt

 

[homeowner123]

Thanks for the replys and suggestions all!

Could you show on one of the pics where the bottom of the external wall is in relation to the inside wall? That will help identify the extent of the bridging.

I've uploaded a photo showing the kitchen step. That at least gives some idea how high the inside floor is above the ground outside.

OP, what youve got is a rendered plinth not a full gable renderin.
Plinths dont usly have Bellcasts.
the plinth was probly instaled in an attempt to prevent dampness - the pointing looks pretty new as well.
hack the plinth off the wall, an clean an point the lowerbrick courses.
look for a DPC while you do it.

I looked for a (slate) DPC inside but didn't see any sign of it unless it is higher up the wall underneath the plaster.

is that a private pathway or the street pavement? that gables wher you needa few air bricks.

It's the street pavement.

I'm still open to the idea of a dropping gutter or drainage fault.

We haven't seen a wide angle, standing-back pic of the side of the house yet.

Will try to upload a photo next chance I get.