Replacing tiles and insulating small pitched bay roof

[Halebop]

Apologies for the long posting, just wanted to avoid people having to ask more questions to get a complete understanding of the situation.

We have a 1.1m x 2.75m roof above a bay window on the ground floor of a 1920’s house with broken clay tiles which also needs new flashing. We are currently renovating the room where the bay window is, and in the process removed the ceiling below and hence have access to this roof from inside too.

We have a stock for replacing broken tiles – but we are aware that we will need to take all the tiles off and re-lay them. It is our understanding that as we are essentially replacing the roof covering we should at the same time upgrade the insulation (in fact there is currently NO insulation). We think we are required to have 140mm min thickness of Cellotex/Kingspan or similar between the rafters. Also there is currently no underfelt below the tiles and we plan to put this in.

We cannot change the pitch or height of the final roof in any way as it is actually a continuous structure going across the front of the house and over to the adjoining house (there is a gable at the remaining end). So we need to maintain the original roof level. We also don’t really want to mess with the original roof frame work. This obviously means that we cannot put any insulation between the tiles and rafters. It is also our understanding that we should have a 50mm air gap and as well as a vapour control layer.

How should we finish the insulation where it meets the eaves? At the moment there is a gap providing ventilation. We want to prevent starlings nesting, as in the past they have got under the tiles and into the roof void. But if we make the insulation board go right down to effectively block this ventilation do we risk condensation?

I'm having problems attaching a picture, but I have a picture in my album on this site of howwe intend to layer all the elements we need. Have we got this right??

Also several other queries;

1. How exactly do we fix the insulation boards – guess a builder’s merchant can answer this?
2. Do we need to ventilate the gable end – and if so what way is best (it is currently just a piece of ply but could easily be replaced)?
3. I have yet to see insulation at the exact thickness we need – is it ok to sandwich boards together or do we have to use the next size in thickness?
4. What should we use to divide off the neighbours roof space bearing in mind that we need to do this, as their section is not insulated to prevent birds nesting? Also will we need to ventilate this division?
5. How do we join the insulation boards together to insure minimum heat escaping between them – I read somewhere that ordinary builders silicone is acceptable?
6. We currently have no counterbatens, only tile batons – is this ok? Again we don’t really want to put counterbatens in as it will affect the final height of the tiles.
7. Do we need a vapour control layer and if so where does it go?

We do want to improve the insulation, but mainly doing all of this to comply to current regulations. We are aware that we require building control approval too. However, are we over thinking the insulation task?

Is it a case of we don’t need to worry too much about meeting regulations as it will not be cost effective in heat conservation terms for such a small proportion of the house?

We are competent DIY’ers and have done lots of work in the past but have never attempted a roof. We have done a fair amount of research but would be grateful for some clarification/conformation that we are going about this the right way.

Many thanks!!

 

[ladylola]

It's all fairly straight forward really.
fixing the insulation ? It can simply be laid in between the ceiling joists so no real need to fix.
Keep the insulation away from the eves by an inch or two to allow for ventilation to occur , wheather or not to do the gable end is up to you probably not really necessary but then it's not going to hurt. If you do just use a small grille backed with fly mesh. The fly mesh should also be fitted to the eves to stop birds and as the name implies insects too.
The join between yours and your neighbours could be done with ply with vents cut in and fly mesh pinned over these vents.
Inulation if it is the kingspan type can be jointed with foil tape and as to the thickness go for what ever size you wish thicker gives more insulation and yes you could build it up from thinner layers it won't hurt.
Don't worry about counter batterns and use tyveck rather than felt.
Hope this helps.

 

[Halebop]

Thank you Ladylola,

We hadn't thought of just using foil tape - that is usefull.

When we said 'underfelt' we were actually thinking of Tyvek or similar so thanks for that conformation.

Someone else has mentioned that we should have a barrier to prevent fire between our part of the roofspace and next-door's, but at present it is completely open. We feel this would be a sensible precaution, but next door recently had their part of the roof re-done (by a proffesional roofer) and they have not put a barrier (or indeed even any insulation!) up.

I'm not sure we will need any mesh at the eaves as the way we plan to put the Kingspan/Celotex boards will mean that there will only be a small (50mm) airgap (with no access to the main void) and surely this won't be a large enough gap for them to nest or roost in?

Thank you for the advice about sandwiching the boards together. As it is only a small area and we have a chunk of Cellotex which is nearly big enough, we don't want to buy a large peice of thick stuff at over £40 when Wickes do smaller thin bits for less than £20 that we can sandwich.

Again thank you for the help!

 

[ladylola]

To form a firestop rather than use ply as I said before use something like supaluks (probably spelt wrong) or a cheaper option would be two layers of 1/2" plasterboard which is good for a hour.
I would advise useing the mesh though.It's not just the starlings you need to think about. Lots of things could get through a 2" gap including birds , mice, bees and wasps and of course many birds. I have strawberrys in a closed in netted area of my garden, the netting being just under a inch and wrens treat it as if it's not there. Just re read your post about there not being access to the main void through the gap? It's the main void that you should be ventilating so it should be open to the gap.