Someone has suggested to us that we could insulate the floors of our Victorian house by lifting the floorboards, putting in battens and boards and laying rockwool over the top before relaying the floorboards. Big sections of floorboards are going to be lifted for plumbing and electric work so this wouldn't be a lot of extra work and wouldn't be too expensive.
It seems like a good idea - is there any reason not to?
Anthony James wrote
Insulating ground floors is less worthwile than insulating roofs and walls. Although the U value of a floor can look good on paper, the actual heat loss depends upon the temperature differential, and in situations with normal radiators or warm air heating, the air temp at floor level can be much lower than at ceiling level due to convection and draughts. It's far more effective to insulate roofs and walls to a good standard before worrying too much about floors.
But overall it is a good idea. At least it will make the floor much less draughty, especially round the skirting boards, and it'll stop that dirt staining you get round the edges of light carpets. While you've got the floorboards up, don't forget to check for damp, rot and woodworm and any other defects with the plates and sleeper walls, and make sure the air bricks are clear.
BTW, it's much easier and cheaper to support the Rockwool on Netlon plastic garden netting fixed to the joists using a staple gun.
Peter
,
Err well depends on the Victorian house, IMO unless you have Really good underfloor ventilation in old house's you could be letting your-self in for big problems later. There is no such thing as rising damp/wet rot,! Only a lack of adequate air flow.
Mark wrote
This is true with or without any insulation, which is exactly why I recommended checking the air bricks. .
No such thing as rising damp? Wet rot doesn't exist? Then please could you tell me what you think is causing my floor timbers to be so wet all the time and damaged by weevils. Why is there a musty smell and what are these black strands all over the place?
Wet rot certainly exists as you describe. A common reason is that the DPC is bridged by the ground outside having been built up over the years, coupled with lack of ventilation.
.andy
To email, substitute .nospam with .gl
It will be a good opportunity to have a look down there so we'll make a decision when we get to it. Thanks
AJ
PS. When did google groups get so smart that it will link a new thread with an old one with the same subject? I'm sure it hasnt always done it.
In article , Anthony James writes
I have done it exactly as you describe, it was a pain to do, but I am happy with the result. No negative effects so far (1yr on). I also sealed the gap at the bottom of the skirting with acrylic sealant. Go for it.
Andy Hall wrote
But if rising damp doesn't exist then why bother with DPC's?
Peter
It can be easier just to cut polystyrene solid foam insulation to size and jam it between the joists. No need for fixing battens or boards. You're not lacking in space down there, so no need to spend extra on Celotex, just Jablite or similar would be fine. Heat losses are low anyway, so I wouldn't be too concerned about cold bridging through the joists either.
Christian.
What are you doing living in my house?? :) In the place I've just bought I've had to spray for woodworm and weevils. Not too much damage thankfully. I'll be tackling the wet rot problem next. Polythene sheeting on the ground under the floor has been recommended.
-Duncan
No vested interest to declare then John? ;)
PoP
Sending email to my published email address isn't guaranteed to reach me.
Solve the rot problem and you'll solve the weevil problem - they are attracted to, eat, and thrive on wood that has been attacked by rot fungi. And voracious little critters they are as well.
Replace the affected joists with pressure treated stuff - I put DP membrane between the bearers and the new joists for good measure.
Also removed about 20 bags of rubble from under the floor and cleared the air bricks. That should help air flow...
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
Been doing it as long as I've been using it (which is a few years). And dontcha just love those See rest of message (1 line) links . But what I really like is when you follow a link from the search engine to the archive and the latter says the article doesn't exist, please check your URL! Still, what'd we do without it, eh!?
And - hey! - you could always bung some Hep2O down there between the insulation and the boards, connect it up to your CH system and get warm tootsies :-)
Yes I know you did, but "checking the air bricks" IMO is not enough you need a small Gale blowing under old houses to keep the 100 year old oh so porous bricks and timber dry. And old builder's practice of dumping waste under floorboards is another recipe for later disaster. I have just filled a 4 cu.mt skip with crap found under my latest buy,
If you take up a floorboard and stick you head below floor level, are you gassed by the smell, or can you feel a breeze blowing.! Its unlikely to be both.
Mark wrote
But didn't you say that rising dampness doesn't exist? See below
I agree. In that sense my advice to check the airbricks didn't go far enough. Fortunately this situation is still quite uncommon.
Ah, now you've changed your tune. At first you said rising dampness and wet rot DON'T exist. Now you are saying that they DO exist but with good ventilation they SHOULDN'T exist, and that "a small Gale blowing under old houses to keep the 100 year old oh so porous bricks and timber dry" renders DPC's unnecessary. And you ducked my question on what causes floor timbers to become damp in the first place. You're not IMM in disguise are you Mark?
Of course rising damp exists, and saying it doesn't only misleads. Floor plates with no damp-proof couse beneath will frequently become damp and subject to rot damage. Yes, good ventilation prevents rot attack, but relying solely on this is a bit too theoretical and ignores practical considerations. As you said, ventilation can become blocked by rubble. It can also be hampered by clogged-up air bricks, building extensions etc. and there are always areas where air circulation is naturally poor. I would feel much happier knowing there is a damp-proof course under the floor timbers preventing them becoming damp in the first place, with or without "a small Gale" under the floor. Dry timbers don't rot.
And, to get back on topic, with a gale blowing around under the floor, there's all the more pressure to provide draught-proofing and insulation. That doesn't sit well with your ventilation only/no-DPC theory, does it?
Peter
Peter Taylor snipped-for-privacy@DELETETOMAILMEclara.co.uk typed
Obviously rising damp/wet rot exists the real question is WHY above floor level.! Well im about to try an experiment, ive had the usual DPC merchants have a look at this house (Ho yes you need a silicon dpc that will be 3k please) and also a surveyor who I think know what he's talking about. The house is early Victorian with no DPC and built on Very wet sub soil, so im digging out to a depth of 1mt under the floor ( having removed all the rubble from previous owners/builders) that's only another 1ft. and doubling the number of air bricks. The floor timber is all in need of replacement so that will be pressure treated, the plaster on the walls is all coming off to be replaced with a membrane that can be plastered over and then decorated immediately. (the house is for let) I'll let you know in another 20 years/6 months if this approach works. ;-)
Isn't every one on Usenet ?
-- Mark's Signature-Free Zone: No random wordy quotations No attempts at infantile humour And no tedious home pages.
In article , Duncan Lees writes
If you reduce the area for the moisture to evaporate, you will make the walls even wetter.
You need a channel round the edge and a pipe to a drain, or a pump if below the drain level.
In a well designed sub floor void there will be sufficient area of masonry to evaporate any moisture emanating from the floor. We have a coal seam basseting under our house, and it carried a continuous stream of water. The bricks sit on permanently wet clay like slip, but there is no sign of moisture in the bricks. Heat and ventilation is the answer.
J.
In article , fred writes
I would suggest that is a very silly thing to do, as would our timber suppliers. I have insulated the cellar ceiling with rockwool, but left six inches clear at each end so the joist ends don't get damp.
J.
In article , Peter Taylor writes
I have yet to see the brick which, unless one end is actually submerged in water, does not have sufficient surface area to evaporate any moisture contained within it. Indeed if you think about it, if bricks were that porous the mortar would never set.
J.
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