Noggins / Dwangs in rafters

[DC5]

Hi folks, we are about to start insulating our cold roof (140mm pir into 195mm rafters with 62.5mm laminated plasterboard underneath).

 

The rafters are 3.4m long and at 600mm centres. The joiner has added 3x2 dwangs in 2 rows across to support the edge of the laminates. This means the 140mm insulation steps down to 50mm thick timber in 2 rows across each side of the roof. 
 

I’ve raised this with him as I’m worried about thermal bridging he says it’s standard practice and has done it this way for years and the 62.5mm laminate underneath will negate and potential bridging issues.

 

Our joiner has done an incredible job so far and we are very happy so not wanting to rock the boat too much but just wanted to check others thoughts on this?

 

many thanks

[markc]

The rafters go all the way through the insulation so how can a noggin make the insulation level worse? Your joiner is right.

[DC5]

Yes but the rafters are 195mm thick the noggins 50mm so there is a void of 90mm behind the noggin with no timber or insulation and I therefore assume a poorer thermal resistance!?

 

 

[Simplysimon]

get him to notch the face of the insulation so it runs continuously

[ProDave]

25 minutes ago, DC5 said:

the noggins 50mm so there is a void of 90mm behind the noggin with no timber or insulation and I therefore assume a poorer thermal resistance!?

So fill the gap behind the noggin either by notching one of the adjacent thick sheets, or a separate piece of thin insulation.

[markc]

35 minutes ago, DC5 said:

Yes but the rafters are 195mm thick the noggins 50mm so there is a void of 90mm behind the noggin with no timber or insulation and I therefore assume a poorer thermal resistance!?

 

 

The insulation goes behind the noggin, you don’t start and stop it either side. If the joiner is fitting the insulation and hasn’t taken it over the noggins then on this bit they are cutting corners

[DC5]

Thanks gents that’s a very good idea I will put it to him! With all the dwangs in and the insulation started how well it will be received….

[nod]

As with 15 mil plasterboard There is no need to add noggings to support the insulated plasterboard 

If your plasterers are doing the insulation they will immediately point this out I would just ask him to take them out 

[joe90]

Rather than noggins I used to use off cuts of ply or chipboard across an unsupported join in plasterboard for a bit of rigidity, yes my plasterer said it was not necessary but I do tend to over engineer stuff (plus it used up scrap off cuts).

Edited September 27, 2022 by joe90

[TonyT]

It’s 62.5mm insulated plasterboard the OP is using.

 

kingspan insulated board for example  should have a lap of timber at least 19mm at sheet joints/ where joints between sheets are unsupported by the timber framing, timber noggins should be installed.

[Tetrarch]

OK - now I'm confused...

 

I've never heard the word "dwang" before so I went a-checking

 

https://en.wikipedia.org/wiki/Dwang

 

Here it's referred to as a "nogging" - I've always thought (and the above posts would tend to corroborate) that it is a noggin. Anyone come across this before or does Wiki need a correction?

 

Regards

 

Tet

[Mr Punter]

5 minutes ago, Tetrarch said:

Anyone come across this before or does Wiki need a correction?

 

All 3 are used.

[Simplysimon]

6 hours ago, Tetrarch said:

Anyone come across this before or does Wiki need a correction?

depends upon where you live

[TonyT]

Dwang is generally a Scottish term for a noggin

[DC5]

Up here we generally always use dwang (I add noggin to be inclusive!!!)

 

just to update this - 

my excellent joiner off his own back notched the 140mm pir under the dwangs so we are all good.

 

As an aside yes they are probably overkill and the ply is an excellent suggestion as an alternative.

 

We are actually fitting 50mm pir over sheeted with plasterboard as it’s easier on this huge roof to lift and also about £15 plus in total cheaper than using a 62.5mm laminate.