Following the boiler efficiency thread, I am exploring the concept of exterior below ground insulation.
As said elsewhere, this house is timber frame on a concrete pad and has only 30mm of foam insulation under the ground floor heating system (Wet underfloor piped).
Any views on inserting say 50mm styrene type foam between the top of the pad and exterior ground level? We already have 150mm depth of pea gravel so not quite soil to wall contact already.
No way of stopping heat going down but a chance of stopping some of it going sideways!
I believe it is only the heat loss through the 1 metre perimeter that really matters for properties built on solid ground (i.e. no suspended, ventilated floors).
There is a quite a bit in Part L, pages 32 and 33 (2002 edition),
Quote.
example 8: Solid floor in contact with ground.
Determine the thickness of insulation layer required to achieve a U-value of 0.3 W/m2K for the ground floor slab with these dimensions:-
Large rectangle 6 x 6 metres Small rectangle 4 x 4 metres
It is proposed to use insulation with a thermal conductivity of
0.025 W/m2K
The overall perimeter length is 10+4+4+2+6+6 = 32m
Floor area is (6x6) + (4x4) = 52m2
The ratio, perim length ------------- = 32/52 = 0.6 floor area
using table A13 column C, row 23 indicates 51mm of insulation.
A13
Thermal conductivity of insulation 0.020 0.025 0.030 0.035 0.040 0.045 0.050 Row P/A . U-value of 0.30 W/m2k .
23 0.60 41 51 62 72 82 92 103 . .
QED, if you property is not a pure rectangle then you have increased the perimeter and hence the heat loss through that all-important 1 mtre band.
The problem with edge insulation is that you have a ventilated? cavity, so there is air movement between your proposed insulation and your slab insulation. I don't believe you will achieve much.
Shielding the property from North/easterly winds with wind breaks like dense hedges or walls might help.
How far down below the DPC does the cavity extend ?, and is there any insulation in it ?. Normally I would expect the cavity to go down at least a couple of block courses below DPC, so about 18 inches and full of all the 'snots' from the building of the inner leaf, possibly.
Sometimes builders fill the cavity up to about one brick course below DPC with a weak mortar mix.
THis is the problem. Between your slab and the outside ground you have a cavity and you don't know what is in it. If it was clean I would fill it below DPC with expanding foam. I don't think you need worry about bridging the DPC with foam. Then some external below ground perimeter insulation might help but this also depnds on soil type. Light sandy soil could benefit from edge insulation, while heavy clay less so (AFAIK)
In 1995 insulation standards were mediocre. Even in 2010-built new houses I have seen 1 inch thick poly inside a cavity and not even tightly strapped to the inner leaf.
The original chalet bungalow is timber frame with the inner 4" leaf filled with glass fibre wool. Plasterboard inner, 12mm ply with waterproof facing outer. I think the cavity is quite narrow with the exterior 4" brick secured with nailed on tabs.
As far as I know, the whole original structure sits on a reinforced concrete pad.
Hertfordshire soils can be anything from clay to light gravel. This house is on a fairly light mix.
In message <QaGfG2g$ snipped-for-privacy@marfordfarm.demon.co.uk>, Tim Lamb snipped-for-privacy@marfordfarm.demon.co.uk> writes
Erratum! I have turned up the original construction specification. Unless building inspector wanted more, the foundation trench is 600mm deep 600 wide, 225mm concrete strip. Blockwork below dpc to be concrete blocks with the cavity filled to 225 mm below dpc.
The sub floor is 137mm concrete over 150mm blinded hardcore and 1200 gauge dpm.
Ok. My 1976 house is not timber-framed and the DPC is at the finished internal floor level. i.e. The DPM overlaps it and then goes down under the slab which is presumably 5 inches thick topped by about 80mm of screed.
I still can't visualise where your slab goes. Does it cross the cavity ?, or did they build up the inner blockwork on the foundations and then construct the slab on the inner leaf of blockwork and then fit the timber framework on top of the slab ?. If so there must be a clear cavity across to the outer brick leaf so any perimeter heat loss goes down the inner leaf and into the foundation. QED The benefit of putting insulation on the outside of the outer leaf will be difficult to measure.
Sorry. This is incorrect. Conventional construction as below.
Indeed. I suppose measuring the exterior wall temperature below ground level might give a clue but, now we have established the existence of a cavity, I am beginning to accept this is likely to be unrewarding.
I guess the best way to look for places where heat is escaping is by acquiring one of those devices that indicates the temperature of a structure using colours. Blue for cold through to yellow/white for hot.
One of the alternative energy companies used to have some that they lent out to their customers for a short period. Can't remember which one it was.
I'd still like to know more about this as potentially this is a DIY job I could do, digging a slit trench and slipping polystyrene down.
Being mostly wood heated I hadn't worried about heat losses when I was younger but now with less access to free wood and the labour of filling the log store beginning to be a bit of a chore losing less heat is appealing.
I did wonder out turning our small (we have combed ceilings) loft into a warm one but all the junk up there doesn't need heating and it involves cladding much more surface area. Also I'm still not convinced of the efficacy of multilayer reflective insulation .
My alternative is lifting the boarding by 100mm and laying an extra roll of fibreglass insulation.
Indeed. I think you need a waterproof material though. Kingspan do an expanded extruded Styrene.
Your floor/wall temperature will be close to room temp. so less of an issue than my potentially 50 deg.C from underfloor heating piping. I mean to dig a hole and try to get actual surface temperatures...
Trees keep falling down here! No log burner now we have sold the farmhouse but a daughter takes any surplus!
The actual heatloss guesstimates for a sold floor with no insulation under are - interesting - and seem to be an estimate of the average path length from the floor through the soil to the outside air.
Obviously the shorter the path length the colder the floor will be. So outside walls are significant paths, but how significant is something I am not going to waste hours of my life calculating.
Yes, but it would be better to have the insulation running from ground level all the way up to the eaves/soffits and over-rendered. Unless you can get a grant (time limit expired last November) it may not be economically worthwhile unless it is a rental and you have to achieve a minimum level of heatloss. Personally I would do the inside, it's much more DIY-able.
Solid walled properties tend to have suspended timber floors so your biggest benefit would be to insulate under the ground floor between the joists with rockwool suspended on chicken wire. Also remember you need airflow under a suspended floor hence the need for insulation below floor level.
The Irish Part L Documents seem to be more comprehensive than ours (100 pages vs 46), with lots more useful diagrams :-
Well that cannot happen as a feature of the cottage is its two coloured brickwork. So straight away there is a cold bridge problem even if I add
90mm of multifoil and dry lining inside.
Yes I suppose one would need to work out pounds spent per Watt saved
In this case it did have suspended floors and we can see the iron underfloor air vents immediately below the slate DPC but all the downstairs is solid floor parquet now and I dread to think how badly it has been done wrt heat loss but in 43 years we haven't suffered damp problems. I imagine the work was done in the late fifties.
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