flat roof noggin dimensions

[Malc]

Hi,

I can't find anywhere that says what dimensions are needed for noggins to support flat roof deck edge. Long edge lines up with rafer/joist. For short edge I read it says fit noggin, but how big? Presumably this depends on rafter/joist spacing. I don't want say size as rafter/joist since this is a cold roof and I need an air gap under the noggin. Can anyone point me towards a table for noggin size?

TIA

 

[^woody^]

I don't understand what you are trying to say or do.

 

[Malc]

In a flat roof you have rafters, say, 50x170. On top of this goes the deck, osb or ply, 2.4 x 1.2m max size. Where 2 sheets on of a roof larger than 2.4x1.2 you need a noggin, between the rafters, to support the edges of the osb/ply. What size wood does the noggin have to be?

Say noggin is 45x45, then for 50 air space above insulation in a cold roof the max insulation would be 170-45-50. I want to know how big I have to make the noggin as that eats into my insulation height.

 

[noseall]

The nogg is only spanning a short distance so can be as little as 50mm x 50mm. If however you were say using the nogg for solid bridging then you would be foolish not to use timber at the same depth as the main joists.

 

[^woody^]

Use a joist offcut fixed flat or some 4x1 flat. Most people don't bother though, as the deck is self supporting with joists at 400mm centres.

Don't forget your furrings, which will give additional space above the insulation.

 

[Malc]

Thanks for the replies. I have remember the furring but they don't make much of difference.

BTW my solution is T&G OSB3, aka roofdeck or other trade names. If I use the long T&G side at 90 deg to the rafters then I don't need a noggin which makes life simple.

Of course I still need strutting but I'm going for herring bond to max insulation and air space.

 

[noseall]

Thanks for the replies. I have remember the furring but they don't make much of difference.

Pourquoi?

 

[Malc]

Because the slope of the roof is 90 deg to rafters so last rafter has 0 furring, next at say 450mm, 1:40 has 11mm.