insulation

[harrison_633]

Hi thinking about insulation can anyone tell me how thick cellotex has to be under a susspended floor.The loft has has about 250mm of glass fibre beetween the joists would i be better off replacing this with cellotex.
Thanks in advance to you helpfull people.

 

[luisdesign]

Ground floor insulation level requirements are worked out using a calculation;

Perimeter / Area = Ratio

The ratio will affect the thickness of insulation you will need in order to meet the current regulations.

As for the loft insulation, the fibre is still doing a job so I see no reason why you should go through the hassle of removing it and putting in new insulation. If you want to improve the insulation of your roof you can always add more insulation (which can be whichever type you want).

Unless you are doing work to your loft such as haivng an extension then it's probably best to just keep it as is.

 

[harrison_633]

Hi thank you for your responce but maths is not my strong point so it sounds dutch to me the area is 6mx5m any help most appreciated

 

[^woody^]

Ground floor insulation level requirements are worked out using a calculation;

LOL

How about ... 200mm rockwool or polystyrene (white), 160 Jablite (yellow) or styrofoam (blue) or 110mm of any of the foil backed types

Edit:

Altered foil backed from 80 to 110mm

 

[^woody^]

.The loft has has about 250mm of glass fibre beetween the joists would i be better off replacing this with cellotex.
Thanks in advance to you helpfull people.

No

Solid board does not fill the gaps which quilt will do, and is a lot harder to fit and mess about with.

Just make sure it goes across the joists too, not just in between

Whether its worth topping up to 350mm, I don't know. If its free/cheap and you like laying insulation, then maybe

 

[mointainwalker]

woody

You have been and continue to be really sloppy about comparative insulation materials.

To provide the equivalent of 100 mm of fibre -wool you need 80 mm of extruded PS ( usually yellow/blue ) or 60 mm of PIR ( colour unknown to me )

The additional benefit of going to 350 mm of fibre-wool is very very small. If energy prices continue upwards, then just very small IMO.

 

[luisdesign]

Hi thank you for your responce but maths is not my strong point so it sounds dutch to me the area is 6mx5m any help most appreciated

This gives you a perimeter of 22m and an area of 30m giving you a P/A ratio of 0.73

This means that in order to meet the current regulations of .022W/m2K you will need at least 110mm thickness (not 80mm) of Kingspan K3 floorboard for example.

Celotex have a number of potential boards that can be used for this application such as the GA4000 or XR4000 but I don't have their datasheets on hand to give you exact thickness requirements. (Now you have your P/A ratio though you can call up their technical department for further advice).

 

[^woody^]

woody

You have been and continue to be really sloppy about comparative insulation materials.

What are you on about?

Those figures I stated are the maximum values required for any perimeter/area ratio calculation for domestic properties, to answer the OP's question

They are not comparative

Doing an actual calculation may lead to less thick insulation, but its not worth it