Investigating wet subfloor

[sealed]

Hi

I’m trying to combat damp under my floor as it sometimes smells musty in the house.

House: 1930s semi. Street level higher than house.

History: MDPE moled to replace lead pipe in 2020. Renovation 2021, including UFH.

Houses nearby get water in suspended floors. During renovation we found almost a foot of water. Builders reinstated a subfloor drain and water company repaired a cracked surface water drain and gully running along the back of the house.

Current issue: house sometimes smells musty near the stairs. This happens here because the only area without screed for UFH is in the cupboard under the stairs. I’ve used this to get in the crawl space and made the map attached and some photographs.

The duplicate photo shows where it is wet. The area by the bay is wet. The area by the front door where the MDPE pipe comes in is very wet. Some joists were replaced as were rotten during the 2021 reno.

ground levels: Outside ground levels are too high. I have dug a trench around the bay. I have taken some pictures. So far it has not filled with water.

DPC: the bay does not have a DPC but the walls around and the sleeper walls that also form a kind of cavity by the bay, have a DPC which is about level with the bottom of the concrete plinth.


please can I have some advice on how to get this area to be dry.

Ventilation has definitely been affected for the worse by the 1950s addition of the garage and the recent renovation. There should be at least two extra air bricks where the bathroom is. And airbrick 7 directs almost directly onto a brick.
But the house (and surrounding houses) having water issues is also a problem. It is too wet under there.

Questions:
1) The staggered sleeper walls in the middle which hold wall plates…would removing more bricks help to cross ventilate?
2) The insulated MDPE is on the floor. It is wet inside and outside of the lagging. Is this normal? How can I fix this?
3) Is surface water leaking through the entry point of the water pipe? Or is the pipe leaking? Anything to be done?
4) Is reducing front ground levels worthwhile? How can it help with this?

Any other ideas?

Thanks

 

[JohnD]

Do the red blobs on your drawing indicate the wet areas?

Clay gullies and drains are usually broken and leaking.

If your moat is lower than the ground under the house, I should think it will catch, and possibly drain away, the excess water.

Looking at the age of your house, I should think it was built with DPCs, some of them are probably hidden, and possibly bridged, by the cement plinth.

Do not allow anybody who sells silicone injections near your house.

 

[JohnD]

(1) If the keeper walls are honeycombed that should be enough. But cut some more airbricks to allow more airflow from one side of the house to the other. One every metre is not too many.

(2) no, there is probably a leak. Might be damage, more often a joint, but polypipe does not usually have many joints.

(3) possibly. Dig it out and have a look.

(4) yes.

 

[sealed]

(1) If the keeper walls are honeycombed that should be enough. But cut some more airbricks to allow more airflow from one side of the house to the other. One every metre is not too many.

(2) no, there is probably a leak. Might be damage, more often a joint, but polypipe does not usually have many joints.

(3) possibly. Dig it out and have a look.

(4) yes.

Thanks. Is the MDPE sitting on the ground of the subfloor a problem? Should it be suspended?

I better get digging.

 

[sealed]

Do the red blobs on your drawing indicate the wet areas?

Clay gullies and drains are usually broken and leaking.

If your moat is lower than the ground under the house, I should think it will catch, and possibly drain away, the excess water.

Looking at the age of your house, I should think it was built with DPCs, some of them are probably hidden, and possibly bridged, by the cement plinth.

Do not allow anybody who sells silicone injections near your house.

The foundations start at the level of the ground under the house. Is it safe to dig the trench to that level? it would direct water directly into the foundations?

I can see the inside of the bay window wall from the crawl space and can’t see DPC but there is a DPC on the kind of cavity wall that is formed. There is slate above the air bricks.

Edited: the dpc is just below the airbricks. Looked closely at the pictures.

 

[JohnD]

Does your house have oversite concrete under the floors, or is it bare earth?

Don't dig below the footings. It can be done (e.g. for basement excavations) but you have to do it in short bays and backfill with concrete. From the age of your house I would have thought the brick walls start to widen at their base, and might or might not have concrete beneath them.

The polypipe can lie on the ground inside the void, but it is supposed to be insulated.

 

[sealed]

Does your house have oversite concrete under the floors, or is it bare earth?

Don't dig below the footings. It can be done (e.g. for basement excavations) but you have to do it in short bays and backfill with concrete. From the age of your house I would have thought the brick walls start to widen at their base, and might or might not have concrete beneath them.

The polypipe can lie on the ground inside the void, but it is supposed to be insulated.

I can see the foundations at The bay from the inside as the ground finishes where the footings start. They are concrete. The subfloor is also some sort of concrete - hard to tell really.

The poly pipe has some type of foam lagging/insulation round it. The pipe on the inside of the insulation is wet and the lagging on the outside is wet as it sits on the wet ground.

 

[JohnD]

A rubbery, black insulation is preferred for underground pipes as it withstands water. From what you describe I suspect the water is coming from a leak or saturated ground. Pipes can also get wet from condensation if they pass through warmer, humid air.

As your house is on a slope, I suppose ground water will run towards the front wall. If you can repair any leaks or breaks this will reduce it. Do you have a gap at the side of the house so you could lead a French Drain to pass it, going downhill?

I once had to build an underground brick wall on the boundary to hold back water from a neighbour who was unwilling to repair his drain.

 

[sealed]

A rubbery, black insulation is preferred for underground pipes as it withstands water. From what you describe I suspect the water is coming from a leak or saturated ground. Pipes can also get wet from condensation if they pass through warmer, humid air.

As your house is on a slope, I suppose ground water will run towards the front wall. If you can repair any leaks or breaks this will reduce it. Do you have a gap at the side of the house so you could lead a French Drain to pass it, going downhill?

I once had to build an underground brick wall on the boundary to hold back water from a neighbour who was unwilling to repair his drain.

No gap at side of the house. There is a water company surface water drain somewhere across the front. Wondering if a French drain across the front garden that connects to that drain would be the best option.

Will definitely look into leaks. Could be the mdpe pipe, the gullies or the surface water pipe that they connect to. Could even be another land drain underneath…

 

[JohnD]

Old clay gullies are broken, more often than not.