TF Studs 38mm x 89mm - too small?

[Hilldes]

Got a quote for timber frame. The supplier appears to have a standard sized stud for exterior walls: 38mm x 89mm (C16 structural softwood). While I don't doubt this is adequate to take the loads, a couple of questions please:

 

• From my research, most other suppliers have studs 140mm or more deep. Is that correct?
• In my specific case, with no brick or block outer skin (render on board), the 89mm stud appears 'insubstantial'. Should that be a concern?  

[ProDave]

I have never seen a TF with 89mm studs for the outside walls.  I would doubt they were strong enough.

 

It used to be common for TF's to be built with 100mm studs but they moved generally to 150mm nearly 20 years ago now.  Apart from anything else with such thin frames, where do you get enough insulation?  Ours is a 190mm frame.

 

 

[Hilldes]

Thanks @ProDave, there is additional insulation across the inside of the studs. Allegedly achieves U-values between 0.19 and 0.13 (assumes a brickwork external skin).

[A_L]

1 hour ago, Hilldes said:

• From my research, most other suppliers have studs 140mm or more deep. Is that correct?
• In my specific case, with no brick or block outer skin (render on board), the 89mm stud appears 'insubstantial'. Should that be a concern?  

 

Yes, but the move to 140mm was originally  to accommodate more insulation in response to building regulations changes.

If you have a lightweight roof then I would have no worries structurally.

A brick/block outer skin has no/little effect on the U-value achieved. To get 0.13 U-value I would expect at least 300mm of fibrous insulation or 200mm of PIR/PUR

[Russell griffiths]

1 hour ago, Hilldes said:

Thanks @ProDave, there is additional insulation across the inside of the studs. Allegedly achieves U-values between 0.19 and 0.13 (assumes a brickwork external skin).

Never. 

Although I know nothing compared to the insulation experts on here I cannot for the life of me see how they are getting those numbers

i think there is a bit of porky telling going on. 

You would need 120mm of internal insulation on those studs. 

 

I think i would give this company a wide berth. 

 

My house in oz was built with 90mm studs and it just felt like a fancy shed,  they do not build over there for longevity 

50 years and bulldoze it and build again. 

[ProDave]

13 minutes ago, Russell griffiths said:

My house in oz was built with 90mm studs and it just felt like a fancy shed,  they do not build over there for longevity 

50 years and bulldoze it and build again. 

My BIL has a 100 year old low set Queenslander that is built pretty much like a shed.  Because of the warm climate, a lot of the rooms have no insulation at all, and on the inside you see the frame, and the inside of the cladding!!!!!  It would not work here.

 

I think termites are a bigger threat to wooden buildings there than the weather and rot.

 

If this house with the 89mm frame needs 160mm of insulation on the inside it is going to make fitting out tricky, lots of long fixings through the insulation into the frame.  I would avoid.

[Hilldes]

Thanks all. I'll see what I get back from other suppliers' quotes.

 

P.S. The quote in this post is from a very well known brand featuring their own insulation products. The U 0.19 variant features 25mm rigid insulation across the internal face of the studs as far as I can tell from the quote only.