Floor insulation with a ventilated crawl space

[JohnD]

Heat loss happens in a building through radiation and convection.

It appears you are not familiar with conduction.

Nor draughts.

And not with heat loss through dwelling floors.

 

[AronSearle]

Heat loss happens in a building through radiation and convection.

It appears you are not familiar with conduction.

Nor draughts.

And not with heat loss through dwelling floors.

I would carefully consider the points you have made.

Except you haven't made any.

 

[JohnD]

I have made my recommendation.

Heat loss happens in a building through radiation and convection.

we are talking here about reducing heat loss through a wooden floor in an existing building with subfloor void beneath. So your "radiation and convection" are not at all correct for the OP's question.

 

[geraldthehamster]

This is all b*llocks, isn't it? Either mineral wool or rigid insulation will be effective, neither is prohibitively expensive. The choice is going to be based on what's most practical for a given situation, not on an abstract consideration of U values, or the physics of heat loss.

Cheers
Richard

 

[AronSearle]

I have made my recommendation.

Heat loss happens in a building through radiation and convection.

we are talking here about reducing heat loss through a wooden floor in an existing building with subfloor void beneath. So your "radiation and convection" are not at all correct for the OP's question.

Convection pulls heat up through the building, as you all described! through the floor.

Non air permeable insulation underlying the floor will greatly reduce this affect, and EPS is a cheap alternative to rigid foam.

I've yet to hear any counter argument other than ad hominem.

This is all b*llocks, isn't it? Either mineral wool or rigid insulation will be effective, neither is prohibitively expensive. The choice is going to be based on what's most practical for a given situation, not on an abstract consideration of U values, or the physics of heat loss.

Pffffttttttt*fart*

Like I said, most people will only lift up a floor once in their lifetime.

Why not make just that little more effort to do a bang up job.

 

[AronSearle]

I have made my recommendation.

Heat loss happens in a building through radiation and convection.

we are talking here about reducing heat loss through a wooden floor in an existing building with subfloor void beneath. So your "radiation and convection" are not at all correct for the OP's question.

Convection pulls hot air up through the building, as you all described! through the floor.

Non air permeable insulation underlying the floor will greatly reduce this affect, and EPS is a cheap alternative to rigid foam.

I've yet to hear any counter argument other than ad hominem.

This is all b*llocks, isn't it? Either mineral wool or rigid insulation will be effective, neither is prohibitively expensive. The choice is going to be based on what's most practical for a given situation, not on an abstract consideration of U values, or the physics of heat loss.

Pffffttttttt*fart*

Like I said, most people will only lift up a floor once in their lifetime.

Why not make just that little more effort to do a bang up job.

 

[JohnD]

Convection pulls hot air up through the building, as you all described! through the floor.

mineral wool stuffed between the joists will stifle airflow and draughts, as well as providing insulation. It is much easier to stuff mineral wool into an irregular gap than to make foam slabs fit tightly.

it will also keep the carpet, if any, cleaner.

 

[geraldthehamster]

Like I said, most people will only lift up a floor once in their lifetime.

Why not make just that little more effort to do a bang up job.

If you're actually going to lift the floor, then it's a no-brainer to use Celotex, cut slightly under size and fixed to the joists with expanding foam. Quicker and less messy to fit, makes a tidier job, and ensures all draughts are eliminated. That's my experience anyway. Have you found it not to be so?

But if I didn't want to take the floor up, I'd be looking at rock wool and netting, as easier to insert into the space.

Cheers
Richard

 

[AronSearle]

mineral wool stuffed between the joists will stifle airflow and draughts

Sorry, no.

Plenty of evidence to show air convection happens within mineral wool insulation, as well as air being pulled through it. Apart from the obvious H&S aspect, you could breathe through a mouth of the stuff.

If you're actually going to lift the floor, then it's a no-brainer to use Celotex, cut slightly under size and fixed to the joists with expanding foam. Quicker and less messy to fit, makes a tidier job, and ensures all draughts are eliminated. That's my experience anyway. Have you found it not to be so?

Yes I agree, but celotex is ruddy expensive.

using a mixture of mineral wool with EPS underneath is cheaper, but more of a hassle to fit, but worth it IMO if you are doing it yourself and have a limited budget.

 

[geraldthehamster]

Yes I agree, but celotex is ruddy expensive.

For reference, it's about 20 quid for a 1200 x 2400 sheet of 50mm Celotex (your builder's merchant may vary). I've no experience buying Rockwool slabs, but this site:

http://www.condell-ltd.com/Page.aspx?catid=1343&gclid=CIKm-OG3xL8CFQQFwwodJKkAYA

has the same quantity of 1200x600x100mm Rockwool insulation slabs for about the same price. I don't know if you'd need 100mm thickness for the same U value as 50mm Celotex (someone here will); if you used thinner, it would be cheaper (and probably adequate in a floor), and I'm sure there are less expensive products.

Cheers
Richard

 

[freddiemercurystwin]

The OP, manzana, hasn't posted for 3 weeks, I reckon he's decided to go and watch some paint dry!

 

[jabuzzard]

You describe exactly how air movement can effect a mineral wool insulated floor, air can be pulled through the insulation through the buildings convection, as well as cold air being blown through the insulation around vents, (which also happens in roofs).

That is not what I said and your understanding of the laws of thermodynamics really is lacking. What happens when it is windy is not that air is pulled through the insulation (that idea is frankly ludicrous) but that the air next to the insulation is continually being replaced with new cold air, and the air that was next to the insulation is moved away outside the building through the air vents. This is what is know as forced convection and is one of the most efficient mechanisms of heat transfer.

This mechanism of cooling happens whatever type of insulation you have installed, whether it be mineral wool, rigid foam or expanded polystyrene.

I would not that prior to insulating my floor the difference between a cold windy day and a cold still day was very noticeable. Afterwards the installation of 100mm of mineral wool (curtsey of npower total cost £6 for the insulation) it is not noticeable. There will be a difference but you don't notice it the same way.

There is some total nonsense about the mechanisms of heat transfer posted on this site.

 

[jabuzzard]

Yes I agree, but celotex is ruddy expensive.

For reference, it's about 20 quid for a 1200 x 2400 sheet of 50mm Celotex (your builder's merchant may vary). I've no experience buying Rockwool slabs, but this site:

http://www.condell-ltd.com/Page.aspx?catid=1343&gclid=CIKm-OG3xL8CFQQFwwodJKkAYA

has the same quantity of 1200x600x100mm Rockwool insulation slabs for about the same price. I don't know if you'd need 100mm thickness for the same U value as 50mm Celotex (someone here will); if you used thinner, it would be cheaper (and probably adequate in a floor), and I'm sure there are less expensive products.

Cheers
Richard

On the other hand you could er use a roll of insulation for a lot less money than bats. That is what I used on my floor. There is no way I was going to lift the floor boards (note added expense of replacing busted ones and replacement screws and nails) and while there was a good crawl space getting rigid insulation through the small access point was a none starter.

 

[AronSearle]

What happens when it is windy is not that air is pulled through the insulation (that idea is frankly ludicrous)

There are a number of articles on this, sadly behind paywalls, so this is all you get.

http://waset.org/publications/2663/...weight-timber-constructions-with-mineral-wool

Why do you think breathable but non air permeable membranes are made, air can be pulled/pushed through mineral wool around vents or holes in construction.

http://www.google.co.uk/url?sa=t&rc...4AKmGXb7q4Rauhllg&sig2=rycVPwyaxS_NKGWDTOgbZg

"With the addition of air movement through the ventilated
eaves, with a wind speed of just 0.15 m/s, the thermal
performance of the eaves area could be degraded
by 900%."

This one is from 1966, so I hope it is not to cutting edge for you

"Measurements reported in this paper demonstrate the increase in heat transfer due to convective air flow that can occur in wood-frame walls containing air-permeable mineral wool insulation with air spaces in contact with both sides. The effect of this air interchange between the air spaces in- creases with increasing temperature difference, air space height and air permeability of the insul- ation. Use of mid-height blocking and higher den- sity insulation thus resulted in some reduction in the heat flow through the insulation, although con- vective effects were still significant. "

http://archive.nrc-cnrc.gc.ca/obj/irc/doc/pubs/rp/rp318/rp318.pdf

it is not noticeable.

It is not noticeable does not mean it does not happen, airtightness standards exist for a reason, heatloss through air permeable insulation can occur due to air movement *within* the insulation as well as heat radiation, using non air permeable insulation instead (or underneath) will greatly reduce this affect.

 

[JohnD]

the article refers to walls (vertical) where there is an air gap between the surfaces and the mineral wool.

Unlike the case here, where there is a floor, and the wool is to be stuffed tightly to block draughts.

No doubt some studies exist, somewhere, of heat loss in typical UK timber floors, over an ventilated void, where insulation is packed between the joists.