Office floor vents under concrete floor

[MetManMark]

All

The two rooms at the front of our house have suspended wooden floors with vents to the front of the property that I have recently cleared out thereby restoring airflow However the 'office' which is to the rear of the property has a solid floor at a slightly higher level than the front rooms. My long term aim is to remove the floor to see what it reveals as I think it is a more recent addition. However, prior to doing that I removed the skirting board to see whether I could see where the vents to the rear of the property went. There are 3 vents on the outside and having removed the skirting it is possible to feel that the go under the concrete floor and through pipes about 3 inches in diameter. These are all fully blocked.

First question - clearly unblocking these pipes would be a good thing to do. How do I go about doing this? I can only wriggle my hand through the small space created by removing the skirting board. I think I need to pull the junk out rather than push it through as I don't know where the pipes go (see Q2).

The pipes head towards the livingroom at the front of the property. However there are big wooden timbers that run under the wall that divides the living room from the office. So where do these pipes go (or do they just run up to the timber and then stop)? What really is the point of the pipes if they only go through the conrete and then stop.

One final thing - there is damp in the office (I think I posted about this before) that is related to the outside ground being higher than the floor in the office.

Any top tips would be very much appreciated.

Cheers
Mark

 

[Flyfisher]

I'd suggest that a set of chimney/drain rods is a fairly essential addition to anyone's DIY armoury and particularly the various accessories to go with them.

My first attempt at unblocking the pipes would be using some chimney/drain rods fitted with a double worm screw. If the contents are quite fine then a drop-scraper attachment would be quite useful as well.

Something like this, though they're quite widely available:
http://www.plumbworld.co.uk/silverline-868723-double-3337-86855

Success will depend on the nature of the blockage, of course, but that would be my starting point.

Regarding Q2, it sounds to me as if the pipes were intended to improve underfloor ventilation to the front suspended floor. Airbricks at the front of the house are all well and good but ventilation will be better if there are corresponding airbricks (or, in this case, pipes) in another wall of the house. Wind will cause slight pressure differences around the house, resulting in a flow of air through the airbricks/pipes, thus improving the underfloor ventilation.

However, if the house is old and/or has been altered over the year then it's anyone's guess as what those pipes are doing today. I certainly agree with your instinct to clear them out though - if possible. Good luck.

 

[MetManMark]

Thanks for your reply. All sounds sensible. I fear that changes to the house have meant that the air can't flow all the way through from the back to the front due to the wood supports for the suspended floor. The rods you suggested look very sensible - the only thing is that we don't have great access so they would have to be very bendy rods!
Cheers
Mark

 

[Penners]

It's anybody's guess where the pipes go. It seems possible that they were installed to maintain crossflow ventilation under the suspended floor, as FF says, but there's no knowing how long ago and how successfully.

I suggest that your best plan is to make every effort to discover where the other ends of these pipes are, before you start trying to clear them out. If you don't, then you could find yourself:-

1. Putting in a lot of work and possible tool-buying expense to no avail, if they turn out simply to stop "blind" somewhere under the concrete.

2. Possibly compacting whatever is blocking them, instead of pulling the blockages out. It would be much easier to push the blockages out from the other end, assuming this turns out to be worth doing.

I would be trying my best to find the other ends of the pipes. If you can't, then they're probably buried in concrete and useless anyway.

 

[MetManMark]

OK - this makes sense. Could I ask though what was the primary purpose of having the vents and pipes under the floor - to vent the office (concrete floor) or the suspended floor in the adjacent living room?
Cheers
Mark

 

[Penners]

OK - this makes sense. Could I ask though what was the primary purpose of having the vents and pipes under the floor - to vent the office (concrete floor) or the suspended floor in the adjacent living room?

Well, I think that's the problem - it's impossible to know. Judging from your description it would seem likely that the purpose of the pipes was to connect the vents in the outside wall of the office to the cavity beneath the suspended living room floor, so that this cavity had crossflow ventilation (you did say that the living room outside wall also has vents, didn't you?). There would be no purpose (that I can discern) in ventilating under a concrete floor.

I'm guessing that the office also had a suspended floor in the past, in which case the vents in its outside wall would - I imagine - have given underfloor crossflow ventilation to both rooms.

But until/unless we discover where the pipes emerge, we're in unknown territory.

As a PS: I presume you're aware of the reason for ventilating under a suspended floor, are you? If the cavity was unventilated, you could could have stagnant air and the possibility of dampness rising from the soil. This would create an ideal habitat for various kinds of rot to take hold.

 

[MetManMark]

Thanks for your posting. I understand the reason for ventilating under a suspended wooden floor - I was just trying to clarify whether putting vents under a solid floor would help the solid floor in any way. We aren't going to have the cash or time to rip the concrete floor up in the near future but should we longer term think about replacing it with a suspended wooden floor? The room is a bit damp - partially due to the ground against the side wall being higher than the floor (to be rectified). Would ripping up the concrete and replacing it help in any way?
Cheers
Mark

 

[Penners]

Venting under a concrete floor seems to me to be (a) pointless and (b) impossible (unless the concrete floor is a block-and-beam construction - which clearly yours isn't), since the concrete almost certainly sits on sand-filled hardcore which sits on Mother Earth. So there's no cavity to ventilate, and for all practical purposes no risk of the concrete rotting.

Your floor may or may not have a DPM under it. But either way, it will still tend to force moisture in the subsoil to travel sideways and soak into the masonry plinth of the house. The extent to which this happens will depend on several factors - the height of your water table, the geology, etc.

Exposing as much as possible of the outside face of this masonry to the air gives this moisture a chance of evaporating away. So reducing the exterior ground level will be beneficial to the building. there is, I'm afraid, no way of knowing whether it will completely solve your damp problem. You just have to do it, then wait and see.

I certainly wouldn't dig up the concrete right away - particularly if you need the money this would cost for other, more important work on the house. Do the soil-level reduction first, then give the masonry a year or so to dry out. Then see how the situation is looking.

 

[MetManMark]

Thanks Penners. It is good to check your thoughts with others. My feeling is that we need to tackle the outside ground level as soon as possible and worry about the concrete floor later. I am convinced that it was done as an attempt to counteract the damp (putting bitumen roofing stuff on the top) and I think that this has probably made the damp on the walls worse in the long run. I think in a year or so I'll rip up the concrete to see what lies underneath.
Cheers
Mark

 

[Penners]

I agree with all that, with the possible exception of your firm plan to rip up the concrete floor. You may need to do that, but I'd be inclined to reserve judgement until you see what success you have with lowering the soil level.

In an ideal world, of course ripping up the concrete would be a desirable plan. But where the house needs lots of work and funds are not limitless, then money should be allocated where it's most needed.

So step by step - see how you go.

 

[Keithj]

A French drain round the outside is (relatively) low cost and will help get standing water away from the walls.

Waterproof stuff is useful if you know where the water is coming from and where it's going. Otherwise, it's as likely as not to keep it where you don't want it.