Another loft insualtion question

[whatknot]

My daughter is about to have her loft insulated, and as the boiler is up there it will require a walkway and she wants some storage for Christmas decs etc

I am getting conflicting advice on the following, when adding walkway/storage over the insulation, do you need to leave a gap between insuation and boards? or no gap?

Some say leave a gap for ventilation to stop condensation, others say don't leave a gap for the same reason

Which is correct?

 

[ChaiLatte]

AIUI, the minimum depth of insulation is roughly 200mm, which is more than the joist depth.

Thus any walkway you make will need something between its underside and the top of the joists.

Sorry if you know this already, but you can use that as a stepping stone to answering your question.

There are many products available to do this (loft legs). We had a discussion on it a few weeks back. The length of commercially-available legs could tell you where the board sits relative to the top of the insulation.

 

[Sideways]

Shoot me for this, but if you're retrofitting, you can put in as much insulation as you find cost effective.
In an area of loft that I use a lot for storage, I screwed some 2x2" timbers along the tops of the joists to increase the depth, laid 2 new layers of 100mm rockwool between and dropped the flooring chipboard down on top. It's s great deal better than the couple of inches of blown glass wool that the house originally had.
The loft space is well ventilated and gets stinking hot in the summers. I don't find an issue with damp.
Insulation settles under it's own weight and time, so you'll likely end up with a gap anyway.

I don't get the impression that loft legs are very stable for regular foot traffic and if so, only if the boards are secured around the edges so that they can't move sideways.

 

[whatknot]

AIUI, the minimum depth of insulation is roughly 200mm, which is more than the joist depth.

Thus any walkway you make will need something between its underside and the top of the joists.

Sorry if you know this already, but you can use that as a stepping stone to answering your question.

There are many products available to do this (loft legs). We had a discussion on it a few weeks back. The length of commercially-available legs could tell you where the board sits relative to the top of the insulation.

It was I who instigated the thread on loft insulation & walkway/storage

The suggested depth is now 270mm, but the depth we are having is 300mm, loft legs were discussed and decided against in favour of using timber to raise the walkway/storage areas to 300mm, but the conflict is some saying leave a gap (so say 310mm) or just 300mm no gap

There is very little insulation at present, it appears there was insulation but the previous owner pinched it

 

[whatknot]

Shoot me for this, but if you're retrofitting, you can put in as much insulation as you find cost effective.
In an area of loft that I use a lot for storage, I screwed some 2x2" timbers along the tops of the joists to increase the depth, laid 2 new layers of 100mm rockwool between and dropped the flooring chipboard down on top. It's s great deal better than the couple of inches of blown glass wool that the house originally had.
The loft space is well ventilated and gets stinking hot in the summers. I don't find an issue with damp.
Insulation settles under it's own weight and time, so you'll likely end up with a gap anyway.

I don't get the impression that loft legs are very stable for regular foot traffic and if so, only if the boards are secured around the edges so that they can't move sideways.

As I just replied to another, we are going for 300mm, loft legs were an option but decided against in favour of timber

 

[eribaMotters]

We moved into a new build bungalow in Sept 2022. It has 200mm deep ceiling joists We have 400mm of rockwool insulation across the loft, except the 6x6m area I had boarded for storage. Under this is 200mm of Celotex foam insulation.

Colin

 

[Terry - Somerset]

My main concern is that if the loft space is better insulated, you need to be confident any pipework and the boiler are adequately protected against freezing. In fairness having the boiler up there probably mitigates the risk somewhat!!

 

[whatknot]

My main concern is that if the loft space is better insulated, you need to be confident any pipework and the boiler are adequately protected against freezing. In fairness having the boiler up there probably mitigates the risk somewhat!!

I was quite surprised to find the boiler up in the loft but apparently it isn't that uncommon

And yes all pipework will be thoroughly lagged and boiler will have a froststat, boiler is being replaced at the same time as a new roof, then insulation then boarding

 

[whatknot]

We moved into a new build bungalow in Sept 2022. It has 200mm deep ceiling joists We have 400mm of rockwool insulation across the loft, except the 6x6m area I had boarded for storage. Under this is 200mm of Celotex foam insulation.

Colin

This is a 1940s/50s bungalow, ceiling joists are a mere 75mm, but thankfully are supported for the most part by brick walls where they mostly need to be