I'm doing a loft conversion which involve using metal joist hangers
(instead of the traditional joists laid onto the inner leave of a
cavity wall) and I am about to fix the chipboard on top of the
structure, but but I've realized that I have probably omitted some
treatment for possible cold bridges from the end of the joists (the
ends fixed on the joist hangers).
In fact I want as well apply some internal insulation using Celotex
boards fixed internally on the whole 4 walls including the loft space.
Clearly I cannot apply such insulation behind the joist hangers
therefore cold bridges are going to be an issue.

What can I do to eliminate/attenuate such cold bridges?

I am thinking of using some flexible insulation like Airtec (airbubbles
plastic stuff similar to that used in packaging with aluminium layer on
both sides) wrapped around the joist hangers and joist ends as well.
Will it work? Or will it make thing even worse?
Any suggestion appreciated.

Thanks

Alex

I can't see how you will get a cold bridge from the inner leaf of a
cavity wall. The cavity is the thermal break.

dg

Well, as you can see I am not to sure of the issue.
In any case there is no insulation in the gap between the two leaves
(that's why I need to install internal insulation) therefore the walls
will be very cold in winter....the joist hanger is attached to them and
"connected" to the warmer air indoor. Wouldn't this be a cause for
condensation?

As mentioned, the cavity is a thermal break which will prevent cold
bridging. Don't confuse a cooler internal leaf with a cold bridge.

Yes the blockwork internal leaf may be cooler than the room, but it
will present no problems with condensation

How are your existing first floor joists connected to the external
walls - most likely in a similar way to this scenario and the same as
the majority of houses in the UK.

dg

wrote:

What can I do to eliminate/attenuate such cold bridges?

I think you are worrying about a non problem. The joists are already on
the internal leaf of the cavity wall. Ultimately they will be under
flooring, carpet etc and will not represent any more of a heat loss path
than any other joist in your house.

Any suggestion appreciated.

Don't worry so much ;-)


--
Cheers,

John.

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