Water underneath block & beam?

[Andehh]

We are building a large bungalow, our garden has a slight incline to the peak of a hill above the property. Prob 5-7m total height change over 60m odd as we look out & up. Block & beam, with around 400-600mm space under the beams. Roof on, windows about to go in. Pretty heavy clay soil under a few feet of typical soil.

 

What we seem to be getting is mysterious water appearing under the garage aspect of the house.   I lifted up a block for the first time in a month, and found there to be about 4" of water trapped there - this has worried me as I expected it to be bone dry as the roof has been on for the couple of months since I last checked. I imagine rest of the place is similar though I cant check as UFH & screed is all in now.

 

I am wondering if it could be a higher water table when it rains heavily, or water flowing down the hill in the soil and then seeping into some of the blocks and puddling under the floor? There back garage wall is very wet from lack of roof guttering, so it would be getting in via this way as well.

 

Air flow is 'fine' to the sub floor - ie; not perfect as we lost a couple of air bricks due to patio changes, but there is still free flowing air in & out to all cavities under the house. No space is without air flow.

 

Is this normal? How do average builds built over winter (like today when we have had 2cm of rain....) cope with the water getting under there and being trapped? 

 

Damp proof was all immaculately installed & maintained, so no risks there.. I'm not sure what I am worried about, just dont like the idea of water underneath? Has anyone ever thought about this themselves? 

 

Many thanks in advance

 

 

 

 

 

[Radian]

6 minutes ago, Andehh said:

Has anyone ever thought about this themselves? 

 

All night, every night...

 

Seriously though, it's not a huge issue - unless it freezes. Chances of that are slim but non-zero. Our house is on a 1:30 slope which is less than yours but water is 'piped in' via a series of Georgian land drains that cut across the field we've built on. The best solution is to run a perforated pipe around the top of the foundation strip and out to a rainwater drain french drain style. We did that on our recent extensions but the original buildings didn't get that treatment. I'm hoping the new drainage (which does connect up via holes in the walls underneath) will take water away from the house and garage.

 

I wish I had acted on it when the house was built because I could see water at the bottom of the cavities as the walls went up 🙄 Having said that, it's 25 years on now and I've not had any problem with it - except in persistent hot weather (ironically) I get a 'damp' smell from the lower side of the house. I put this down to the ground below drying out and the humidity finding it's way up the back of the dot & dab plasterboard. 

[ProDave]

Do beam and block floors not have a concreted "solum" with DPM as you do with a timber suspended floor?

[Bramco]

You need worry....

 

When we lived in Holland, our plumber had to don a wetsuit to do some connections under the floor for a new kitchen.  A few feet of crawl space with quite a lot of water.  He said it was far worse further to the west of us  - for example in Leiden, where they sometimes had to use blow up boats to get around under the floors......

 

Simon

[Andehh]

Not sure what a solum is?

 

The walls are cavity built off the foundations, with 100mm thick polystyrene insulation below DPC (so 300mm+ to bottom of beams which sit on DPC + blocks which sit on DPC as well). Beam & block then sit on inner wall, with twin breeze block built from here upwards with Knauf dritherm in the cavity. If that makes a difference?

 

It's a full block built house, no timber until you hit the roof.

 

Edited November 21, 2022 by Andehh

[ProDave]

Not understanding the floor build up?  Diagram?  I thought the beams span wall to wall infilled with blocks so where does the insulation under the B&B floor fit in?  Surely that needs to be a ventilated space?

 

Yes you are right I have never looked at a B&B floor between but I would have assumed the same principles as a timber suspended floor apply that you have a DPM and a thin layer of concrete to seal the under floor space (solum) and that is above outside ground level and ventilated so something has gone wrong if it manages to fill up with water.

[Radian]

I think it's the lower part of @Andehh's cavity wall that's (thankfully) filled with XPS up to DPC and dritherm above. You wouldn't want that wicking up standing water from the tops of the foundation. Generally they don't bother with a DPC + concrete on the ground (solum) below B&B - just a layer of type one to make it look pretty for the BCO. I even raked some of that off to make better use of it elsewhere.

[ProDave]

6 minutes ago, Radian said:

Generally they don't bother with a DPC + concrete on the ground (solum) below B&B - just a layer of type one to make it look pretty for the BCO.

Wow.  that sounds a pretty poor detail.  I take it this is because concrete beams and blocks don't bother about a damp humid environment as much as timber would? but I don't think I would be happy knowing it could be a wet muddy mess under there.

[Radian]

16 minutes ago, ProDave said:

Wow.  that sounds a pretty poor detail.  I take it this is because concrete beams and blocks don't bother about a damp humid environment as much as timber would? but I don't think I would be happy knowing it could be a wet muddy mess under there.

 

I know. It's basically just outdoors down there. Don't want to make it too cosy. It's actually a pity to have to have the cross-ventilation washing cold air across the underside of the B&B but if it was all airtight, methane, radon, gas leaks etc. could do nasty things.

[saveasteading]

2 hours ago, ProDave said:

concreted "solum

Much more a Scottish than English thing. 

 

[saveasteading]

Maybe it is just me, but I think of what a drop of water will do.

If it gets in how do you let it out again. Downhill is essential and is really all that matters, along with gaps and somewhere to go next.

[crispy_wafer]

ours was the same, however, the areas where the water was pooling /gathering was around the edges where the builder hadn't filled in.  I know I live in an area that has quite a variable water level, due to slow draining ground more than anything.  I figured the water ingress was seepin in between or through the trench blocks and via the openings that had been created for the service ducts etc.  I spent a weekend lifting the blocks on the b&b floor, then on the tractor loading wheelbarrows whilst the missus and boy spread MOT under the beams (Looks bloody good, and when I had to go tunneling for a lost hammer, i didnt come out covered in mud, so that was a bonus).  The builder thought I was mad for doing so quite honestly, they dont tend to bother with these details.  It looks a lot better, and for the sake of a few hundred pounds worth doing and justified in my mind.  I've also put in some drainage around the property about 10m away or so from the build over the last year or so, basically 4ft deep trenches wrapped and filled with 4-6" limestone chunks leading off to a drainage ditch.  Just to give the water somewhere to go. 

 

Logically once your DPC, and DPM is down your habitable area is a damp proof box, and going about things as slowly as I have, I've seen the seasons pass, dry and wet alike and not seen or noticed any issues.  All is good, and I have no worries.

 

These was taken after a wet spell, albeit we had no walls or roof at the time, so it was likely to puddle...

 

 

 

Lifted them blocks more times than I care to remember.

[George]

Dig a land drain around the house at the top end to divert water away.

 

And knock through a land drain at the low end to let anything that does get in, out. Makes a nice little run for the rats though.

 

It shouldn't degrade the structure but trapping water is rarely a good idea.

[Andehh]

Thanks for the posts all & Crispy_Wafer ...I imagine that was back breaking work, & trapped fingers with those blocks is a memory I care to forget....

 

 

I think I'm pretty much left to accept it. There are only two 'cavities' under the house accessible to pump it out or inspect, other 5 are now sealed up, so unknown amounts of water / nout I can do.

 

Fortunately, I know how utterly OCD the builder was with the damp proofing, though I will look to do some land drains over the worst part of it.

 

Thanks again

[Dave Jones]

normal.

 

nothing to worry about.

[saveasteading]

6 hours ago, Dave Jones said:

nothing to worry about

Perhaps not. But it isn't to be preferred and could be a problem.

I would guess that a porous stratum in the ground (or an old drain, or a void created by a root) has created a path for rainwater. Then somehow it gets through the mortar...it wouldn't need much gap.

Letting it out on the downhill side is easy, using an airbrick. But I wouldn't want it flowing through so would want to catch it at source and divert.

 

[Dave Jones]

you could try and divert - if possible, but still nothing to worry about.

[saveasteading]

If you can crawl around underneath, then it is worth spreading heavy polythene over the surface. Then the water will be underneath it and general wetness and humidity should reduce.

Assuming the ground is wet, not underwater: let that water out.

[Andehh]

The water is only a couple of inches so actually sits within the foundations, below the block surrounds, so no real way to drain it out.

 

I will prob try & pump it out, and see if it returns. We are 4/5 the way up a hill, so in theory water should be draining down & away, as our ground water cant be that high, I hope!! 

[saveasteading]

4 hours ago, Andehh said:

will prob try & pump it out

You can easily entomb a pump, in a sump preferably, and it will kick in occasionally. I've done that a couple of times, with client permission, with great sucess. Whether they still work or the streams closed themselves off i don't know, but expect the latter.