Suspended timber floor insulation


S

stuart noble

I'm looking for ways of insulating a ground floor (bare boards) from the
musty cellar beneath it. Stopping the cold air coming up through the
boards is the main priority, but I'm wondering how effective Rockwool
slabs between joists would be against the earthy smell. Would I need a
vapour barrier as well? In other words I suppose, how do smells travel?

I know I could use Celotex, but it does seem like overkill for this
application, and it's a big old cellar.

I also know I could spend a few grand on the cellar, but there is a
water table issue here that I suspect will just have to be lived with.
 
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T

The Natural Philosopher

stuart said:
I'm looking for ways of insulating a ground floor (bare boards) from the
musty cellar beneath it. Stopping the cold air coming up through the
boards is the main priority, but I'm wondering how effective Rockwool
slabs between joists would be against the earthy smell. Would I need a
vapour barrier as well? In other words I suppose, how do smells travel?

I know I could use Celotex, but it does seem like overkill for this
application, and it's a big old cellar.

I also know I could spend a few grand on the cellar, but there is a
water table issue here that I suspect will just have to be lived with.
So, cheap, anti pong, and mildly isnlating?

If you don't care about looking at the boards. ou can do a very fine
sealing job with hardboard tacked over..after banfging down any loose
nails. This makes a decent base for fitted carpets, vinyl or laminate
over, and will reduce airflow to almost zero.


If you want to preserve the boards visually, you need to do something
underneath as far as airproofing goes: I would use something like foiled
plasterboard or thin MDF tacked under the floor joists, and sealed again
with something like duct tape, with a load of rockwool in between. How
you hold that up I don't know: maybe staple a DPM membrane up
first...that would obviate the need for foil backing
 
S

stuart noble

The said:
So, cheap, anti pong, and mildly isnlating?

If you don't care about looking at the boards. ou can do a very fine
sealing job with hardboard tacked over..after banfging down any loose
nails. This makes a decent base for fitted carpets, vinyl or laminate
over, and will reduce airflow to almost zero.

There was laminate there until recently, but the earthy smell got
through somehow
If you want to preserve the boards visually, you need to do something
underneath as far as airproofing goes: I would use something like foiled
plasterboard or thin MDF tacked under the floor joists, and sealed again
with something like duct tape, with a load of rockwool in between. How
you hold that up I don't know: maybe staple a DPM membrane up
first...that would obviate the need for foil backing

I was thinking about stapling a dpm between the joists but it would be
very labour intensive. Maybe I could stick the Rockwool in non bio
degradable bin liners.
 
T

terry

I'm looking for ways of insulating a ground floor (bare boards) from the
musty cellar beneath it. Stopping the cold air coming up through the
boards is the main priority, but I'm wondering how effective Rockwool
slabs between joists would be against the earthy smell. Would I need a
vapour barrier as well? In other words I suppose, how do smells travel?

I know I could use Celotex, but it does seem like overkill for this
application, and it's a big old cellar.

I also know I could spend a few grand on the cellar, but there is a
water table issue here that I suspect will just have to be lived with.
Sounds like that cellar needs ventilating? And floor needs insulating
and being vapour barriered on it's upper (warm) side?

We ran into such a situation a few days ago.
An undamproofed earth floor, no ventilation, lots of dampness and
insects. Also some signs of incipient rot! Everything down there was
damp and chilly and rank! And the seller didn't seem to think there
was a problem!

There was insulation between the joists of the wooden floor above but
no adequate vapour barrier on the 'warm' side above that (i.e. the
flooring above it). Not only that there was some completely useless
plastic sheeting on the bottom of the joists (the wrong side) some of
which was hanging down because it had collected a weight of moisture!

Not a good situation and we think we will reject buying that property
in view of the potential future problems and costs to correct.

One idea for the OPs situation might be to insulate the floor; use
some type of floor covering that is a vapour barrier (warm side).

Then use a 'permeable building paper' type product stapled or held up
by thin wooden battens, to the bottom of the studs below. Some brand
names for such a product, depending what country you are in are;
Tyvar, Tyvec ...... etc. Other types are a tarry sort of paper that
have many minute holes which do not allow water in but allow the
insulated floor to breathe out any moisture that condenses in the
insulated space.
 
S

stuart noble

terry said:
Sounds like that cellar needs ventilating? And floor needs insulating
and being vapour barriered on it's upper (warm) side?
The ventilation is fine, and the joists and boards above are nice and
dry, so the conditions down there don't seem to be affecting the
structure of the house. As I said, there's a water table issue here
because the adjoining houses also have water in their cellars at the
same time, although actual floods can apparently be years apart. Hence I
don't feel inclined to suggest any action re the floor.
We ran into such a situation a few days ago.
An undamproofed earth floor, no ventilation, lots of dampness and
insects. Also some signs of incipient rot! Everything down there was
damp and chilly and rank! And the seller didn't seem to think there
was a problem!

There was insulation between the joists of the wooden floor above but
no adequate vapour barrier on the 'warm' side above that (i.e. the
flooring above it). Not only that there was some completely useless
plastic sheeting on the bottom of the joists (the wrong side) some of
which was hanging down because it had collected a weight of moisture!
I wonder why moisture had collected there.
Not a good situation and we think we will reject buying that property
in view of the potential future problems and costs to correct.

One idea for the OPs situation might be to insulate the floor;
No, those floorboards are so good, I'd have trouble persuading them to
cover them up
 
M

Martin Hind

I'm looking for ways of insulating a ground floor (bare boards) from the
musty cellar beneath it. Stopping the cold air coming up through the
boards is the main priority, but I'm wondering how effective Rockwool
slabs between joists would be against the earthy smell. Would I need a
vapour barrier as well? In other words I suppose, how do smells travel?

I know I could use Celotex, but it does seem like overkill for this
application, and it's a big old cellar.
Faced with exactly the same problem we settled on 80mm Kingspan cut
to size and held in place as needed with 50mm nails driven partly
home.

I considered a vapour barrier to eliminate draughts but without
lifting the
boards it seemed impossible to fit satisfactorily. The Kingspan fits
so
tightly that draughts are no longer a problem.

The final point in favour of rigid foam is that come an inevitable
spill it's
most moisture resistant. Can't see soggy Rockwool working too well.

HTH

Martin
 
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S

stuart noble

Martin said:
Faced with exactly the same problem we settled on 80mm Kingspan cut
to size and held in place as needed with 50mm nails driven partly
home.

I considered a vapour barrier to eliminate draughts but without
lifting the
boards it seemed impossible to fit satisfactorily. The Kingspan fits
so
tightly that draughts are no longer a problem.

The final point in favour of rigid foam is that come an inevitable
spill it's
most moisture resistant. Can't see soggy Rockwool working too well.

HTH

Martin
Did you have the musty smell, and did it do the trick?
I'd love to fit 80mm foam but I can't see the budget stretching that
far. Do you think it'll be cost effective for a ground floor?
 
G

George \(dicegeorge\)

but
if theres no damp proof membrane under the floorboards
don't you get dampness from condensation along the joists
about halfway through the kingspan
which could rot the wood?


--

[george]


someone write:
 
T

The Natural Philosopher

George said:
but
if theres no damp proof membrane under the floorboards
don't you get dampness from condensation along the joists about halfway
through the kingspan
which could rot the wood?
you could.

The route is really via the wood itself only though, so it should be
fairly minor.
 
G

George \(dicegeorge\)

so should one seal any gaps with foam
(to stop moist air getting through and condensing at the dew points)
or leave gaps for any condensation to trickle down?
~ ~
 
M

Martin Hind

Did you have the musty smell, and did it do the trick?
I'd love to fit 80mm foam but I can't see the budget stretching that
far. Do you think it'll be cost effective for a ground floor?
We have a full sized cellar which is fairly well ventilated and
fortunately not too musty so can't comment on that. As far as making
the house *seem* warmer it's worked well.

Cost effective? That's a tricky one. So for thermal conductance
Kingspan Insulation have very useful information on their website in
the product data sheets - you could calculate the U-value of your
existing floor (which depends on perimeter to area ratio) and the U-
value of your proposed scheme, and thus estimate the improvement in
energy loss based on some assumptions about temp differential and how
many days the heating is on.

Heat loss tends to be higher upwards than downwards, so the benefits
might not be that great. The improvements in air tightness might be
worth it though.

In the end we aimed to meet building regs standard for the renovation
of thermal elements - it's about doing the best one can I suppose.

Good luck

Martin
 
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T

The Natural Philosopher

George said:
so should one seal any gaps with foam
(to stop moist air getting through and condensing at the dew points)
or leave gaps for any condensation to trickle down?
~ ~
Definitely :)
 
S

stuart noble

Martin said:
We have a full sized cellar which is fairly well ventilated and
fortunately not too musty so can't comment on that. As far as making
the house *seem* warmer it's worked well.

Cost effective? That's a tricky one. So for thermal conductance
Kingspan Insulation have very useful information on their website in
the product data sheets - you could calculate the U-value of your
existing floor (which depends on perimeter to area ratio) and the U-
value of your proposed scheme, and thus estimate the improvement in
energy loss based on some assumptions about temp differential and how
many days the heating is on.

Heat loss tends to be higher upwards than downwards, so the benefits
might not be that great. The improvements in air tightness might be
worth it though.

In the end we aimed to meet building regs standard for the renovation
of thermal elements - it's about doing the best one can I suppose.

Good luck

Martin
Thanks, Martin.
 
T

The Natural Philosopher

George said:
definitely gaps
or definitely no gaps ?????
~ ~
Aye, theres the rub :)

Should we stop water getting in, or allow it an easy way to get out.


If you are a Period House Believer, the latter is of course what you do.

Modern houses adopt the former approach.

Either keeps thing dry..
 
T

terry

terry had written: ..

No, those floorboards are so good, I'd have trouble persuading them to
cover them up- Hide quoted text -
Terry says: Sorry to be unclear; meant to say insulate 'under the
floor' using some form of insulation that would stay up underneath and
between the joists. Over here 'they' say it should be close up
underneath against the bottom of the floor etc. That sometimes can be
a problem, at least as a retrofit, cos of pipes wires etc. can be

However depending on what the heat loss might be to that presumably
ventilated but unheated space below it might/might not be economic?
This house has uninsulated main floors over a mainly unheated,
unfinished fully in ground basement that is dry, has a full concrete
floor (area is a subdivided 40 by 35 feet) and is used for storage
and workshops; the basement maintains 50 to 60 deg F summer and
winter: And the main floors are not that chilly although doubtless
insulation would reduce heat loss. But then one might have to put some
ancillary heat in the basement!
 
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S

stuart noble

terry said:
Terry says: Sorry to be unclear; meant to say insulate 'under the
floor' using some form of insulation that would stay up underneath and
between the joists. Over here 'they' say it should be close up
underneath against the bottom of the floor etc. That sometimes can be
a problem, at least as a retrofit, cos of pipes wires etc. can be

However depending on what the heat loss might be to that presumably
ventilated but unheated space below it might/might not be economic?
This house has uninsulated main floors over a mainly unheated,
unfinished fully in ground basement that is dry, has a full concrete
floor (area is a subdivided 40 by 35 feet) and is used for storage
and workshops; the basement maintains 50 to 60 deg F summer and
winter: And the main floors are not that chilly although doubtless
insulation would reduce heat loss. But then one might have to put some
ancillary heat in the basement!
I'm coming to the conclusion that, in this case, insulation is less
important than stopping draughts, but finding something that's easy to
fit between the joists is difficult. 25mm foil backed foam may be the
best compromise.
 

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