Pitched roof ventilation

[Hugh1983]

Untitled

• Hugh1983
• 14 Dec 2011
• 1

Untitled

• Hugh1983
• 14 Dec 2011
• 1

Hello,

I am insulating my pitched roof. This space will form part of the room in the top of the house and therefore there is no loft space. I have been insulating with 50mm ecotherm which is sheet insulation (like celotex or kingspan).

Please advise me if I should simply insulate and tape the sheet insulation up to the very top of the roof on both sides?

I was under the impression that I should possibly leave gaps at the top of the insulation (along the lines of the 2nd picture... and possibly leave more of a gap) and construct and insulate a small ceiling at the top of the pitch which would leave a small void in the top of the pitched roof where the air can circulate between both sides??

 

[RedHerring2]

What is the existing roof lined with?

If it's felt under the tiles, you need a 50mm air gap minimum.

My understanding is:

You must do at least two things: have a "ceiling" for air circulation, and add ridge vents. (I'm assuming you already have eaves ventilation.)
Alternatively you could add slate/tile vents high up near the ridge.

The air will not move up one side of the roof, then down the other. It will move up the roof on both sides, and it can only do that with ridge vents fitted. They are not cheap, about £45 each. They must be fitted correctly, i.e. it's pointless fitting them if they're not done properly.

Incidentally, it can also help if you can prevent any moisture entering the roofspace, e.g. installing a vapour barrier above or below the ceilings to the rooms immediately below..

 

[Hugh1983]

Yes its felt so I'm aware of the air gap needed.

The roofer fitted 4 slate vents to the roof.

So.. im gathering that i will need this small ceiling to the room and allow air to ventilate above rather than taping and plastering all the way up to the top on each side which would leave no air connection between each side of the roof?

 

[Alastairreid]

You insulate to the top of the rafters, no need for a lowered ceiling.
Ventilation is both at low and high level either side of the roof.

Vented ridge and soffit or vent tiles top and bottom.

 

[RedHerring2]

This is not meant as a disagreement, Alastar, more of a clarification, beraing in mind that I'm only a DIYer.
If the OP insulates all the way to the ridge board, surely he must ensure that each and every space between rafters is ventilated via high level vents? I'm assuming he has dwarf walls at the lower end allowing some air movement behind them.
Whereas, if he installed a slightly lower ceiling allowing air movement above it, he wouldn't need to install so many vents. Perhaps reducing the number of vents by half?

 

[masona]

Yes you're right, it's best to put in a small ceiling just below it or whatever minimum height regs so the whole section is ventilated and IMO more pleasing to the eye than a pointed roof and a stronger roof

 

[Alastairreid]

Agree wholeheartedly with both of your methods, i was just pointing out there is no requirement to lower the ceiling at the at the peak providing there is sufficient ventilation installed.
My preference is over fascia vents and ridge vents if practicable.

Better for lights as well