Conservatory Rafter Insulation Advice

[IamOnStage]

We have a glass top wooden framed conservatory roof and will be getting this replaced with slate tiles very soon. To cut on costs I will be insulating with Celotex boards or similar, plaster-boarding and skimming the underside myself but would like to check my plans with you guys!

Bearing in mind that "The warmer the better!"

I have two queries 1) How to insulate, 2) How to ventilate

---How to Insulate---
The rafter depth is only 85mm so for the insulation I believe my two options are:
1. Batten down the rafter to increase depth and insulate between
2. Insulate (50mm) between and insulate (~50mm) underneath rafters - my concern with this option is the thickness of the insulation underneath and how to then fix plasterboard through the underneath-insulation onto something.

---How to Ventilate---
How do I ensure that adequate ventilation will be achieved?

The roofer will be using a breathable felt across the rafters and then batern on top for the slate tiles.

1. Do I need an air gap between the insulation and the felt? (he says we don't)
2. What is the smallest air gap I can get away with to increase insulation depth? (if necessary)


---Side Question---
I have previously fitted plasterboard against insulation boards leaving no gap. BUt for this install I will be fitting spots in the ceiling. What are your opinions on this? Would a gap be good for spots and or cable access?


Thank you for your answers!!

Untitled

• IamOnStage
• 7 Oct 2014
• 1

Untitled

• IamOnStage
• 7 Oct 2014
• 1

Untitled

• IamOnStage
• 7 Oct 2014
• 1

 

[freddiemercurystwin]

You have timber rafters going in right?

Assuming they are being replaced and your membrane is going to be breathable you need a minimum 25mm air gap between your insulation and the underside of the battens. Your roofer is wrong plain and simple.

So 50mm insulation between the rafters will leave you the required 25mm. Screw your continuous 50mm layer up with screws into the rafters, fit your plasterboards up with screws into the rafters. They just have to be long enough.

 

[catlad]

why not just build a new false ceiling and then you can have as much insulation as you like.

 

[rednev]

interested in doing a similar job, wondered how you got on?

 

[theprinceofdarkness]

Do not use halogen spots (30 or 50W), if they are imbedded in insulation they will over heat and the foam may catch fire. Lash out and buy Philips LED spots (7 or 9W) which have a much longer life then ordinary bulbs.
With such a thin ceiling space you might have a problem getting anything to fit. Also the wiring will have to built in with the ceiling.
To overcome lack of depth for mounting lights, I have made superficial pods by cutting a "washer out of MDF with a router with a tapered cutter. Doing the outside first by rotating the router around the centre. Then cutting the centre out with a jigsaw as the fitting will hide the cut edge. paint it in with the ceiling.
Frank