Sunroom ceiling insulation

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Birroc

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I was caught on the hop for the sunroom ceiling insulation. The sunroom is a seperate roof space to the main house - there will be no access to it once it is slabbed and plastered next week.

So I need to insulate it asap. I have no research done on this yet so can anyone send me suggestions on :

a) Type of insulation
b) Thickness
c) Possible cost

It will probably be a cold room in winter so I am thinking above building spec insulation whatever that may be.
 
the minimum u value is 0.2

this can be normally achieved in traditional construction by installing 130 pu insulation.

* NB remember you need to maintain a 50mm air gap between the insulation and the felt for ventilation purposes.

therefore the make-up is dependant on the rafter size... what size have you??
you can insulate between and below rafter, or insulate between and above.. depending on what finish you want.
 
Thanks Syd, Rafters are normal 9 x 2 I think.
I was just going to throw insulation on above them but will I be able to insulate between them without the slabs being in place ?
I was thinking 300mm of the fibreglass stuff.
 
you wont be able to get 300mm in if your rafters are 9 x 2 (225 x 44) becaus eyou require 300 + 50 air gap therefore you would need to counterbatten with 125mm timbers... which is huge.

9 x 2 rafters for a separate sun room sounds big, are you sure??

is your sun room hipped or gabled?? is it square or hexagonal?

the best option may be to install board insulation between rafters and slab under with composite insulation boards.
 
sydthebeat said:
you wont be able to get 300mm in if your rafters are 9 x 2 (225 x 44) becaus eyou require 300 + 50 air gap therefore you would need to counterbatten with 125mm timbers... which is huge.

9 x 2 rafters for a separate sun room sounds big, are you sure??

is your sun room hipped or gabled?? is it square or hexagonal?

the best option may be to install board insulation between rafters and slab under with composite insulation boards.
Click to expand...

Sorry Syd, I meant the joists are standard 9x2. I am not putting insulation in the rafters (I think), just on the joists which will leave loads of room. My sunroom is a normal extension with a normal roof space - did i give you impression the roof of sunroom was arched ? Sunroom is gabled and square.
 
ok, thats fine then, just do the same as you are doing in the main roof... 300mm rockwool is fine.. the actual u value to meet is 0.16

i thought you were insulating up on the slope..... doh! my bad....
 
sydthebeat said:
ok, thats fine then, just do the same as you are doing in the main roof... 300mm rockwool is fine.. the actual u value to meet is 0.16

i thought you were insulating up on the slope..... doh! my bad....
Click to expand...

No worries Syd, 300mm rockwool it is. some people suggest more than 300mm though.
 
300 is the minimum, go to 400 if youd like, budget permitting of course, but youd be much better off making sure that the construction is air tight.
 
Sydthebeat,

Slightly off topic, but still regarding sunroom insulation. Isn't it the case that most sunrooms have one internal wall that is part of the main houses external wall. Lets say a single story sunroom is built onto the gable of a two story house.
This could mean that the cold and damp from the part of the wall that is external and exposed could make the internal wall in the sunroom cold and possibly even damp?
Is there a practice to reduce this effect?
 
yes johny, you are correct. There is a large cold bridge where an outerleaf becomes an internal wall. There should be a damp issue if the junction is properly dpc'd and flashed, but there may be an issue with condensationdue to this cold bridge.

With a traditional cavity wall theres really very little you can do.
One option is to slab this wall with insulation backed plasterboard.
Another may be to build the external wall on top of a steel frame / lintel and insulate under.

There are options if you go with other construction systems.

Most chimneys create these cold bridges as well.
 
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