Internal wall insulation around first floor joists

[John D v2.0]

I think your argument woody depends on the fact that a thermal bridge is an absolute concept. In fact thermal bridging is a relative thing and is usually used to mean somewhere you get black mould. It is also used when calculating u values but normal people are not concerned with that.
A common situation for thermal bridging and mould is where a cavity wall is uninsulated and has no mould, but then the wall is insulated but can't be at the top or under windows or some other hard to treat place. Since the difference is now great, an area that wasn't a bridge before becomes a bridge, and since it's a cold spot gets condensation and mould.

Edit: I should be clear that in this case I agree it's not a thermal bridge, but I haven't done any condensation risk analysis to support that.

 

[^woody^]

I think your argument woody depends on the fact that a thermal bridge is an absolute concept

That's because it is absolute and not a concept. There is thermal bridging or there is not.

It's not to be confused with cold spots and condensation forming, which can be caused by thermal bridging but are not specific to it.

 

[Nige F]

It's just a bridge too far.

 

[^woody^]

It would a pier so

 

[John D v2.0]

well I'm not interested in a comptition of stubbornness, so for anyone who trusts the BRE, here's their definition https://www.bre.co.uk/certifiedthermalproducts/page.jsp?id=3073

 

[^woody^]

That's cleared that one up then. The insulation in the diagram is the air cavity in the OP situation.

Let's have no more stubborn denial of that.

 

[Kealan]

That's cleared that one up then. The insulation in the diagram is the air cavity in the OP situation.

Let's have no more stubborn denial of that.

"A thermal bridge, also called a cold bridge, is an area of a building construction which has a significantly higher heat transfer than the surrounding materials."
E.G. If you were to have timber joists poking through insulation. As opposed to hanging your joist hangers off the PIR board of course.

"This is typically where there is either a break in the insulation, less insulation or the insulation is penetrated by an element with a higher thermal conductivity"
Like if your insulation was penetrated by a joist.

You're correct in that there is no thermal bridge to the external leaf. There is, however, a thermal bridge to the cold side of the internal insulation. The OP has a heat path directly from the warm side to the cold side of his insulation. That's still a thermal bridge; it's just not a thermal bridge to the outer leaf.

 

[^woody^]

"A thermal bridge, also called a cold bridge, is an area of a building construction which has a significantly higher heat transfer than the surrounding materials."
E.G. If you were to have timber joists poking through insulation. As opposed to hanging your joist hangers off the PIR board of course.

"This is typically where there is either a break in the insulation, less insulation or the insulation is penetrated by an element with a higher thermal conductivity"
Like if your insulation was penetrated by a joist.

You're correct in that there is no thermal bridge to the external leaf. There is, however, a thermal bridge to the cold side of the internal insulation. The OP has a heat path directly from the warm side to the cold side of his insulation. That's still a thermal bridge; it's just not a thermal bridge to the outer leaf.

The front door is a thermal bridge then?

 

[freddiemercurystwin]

He'll never admit it, he's like an old warship, refusing to sink despite being continually torpedoed!

 

[^woody^]

Bobbing along on the crest of a wave.

 

[catlad]

Penetrating the insulation with a joist is a cold spot not thermal bridging unless its something like the joists of a flat roof being used to hang the fascia/guttering.

 

[freddiemercurystwin]

Oh God, just let the thread die!

 

[^woody^]

 

[freddiemercurystwin]

Two wrongs don't make a right.