Are Standard Timber Purlins also Thermal Breaks?

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Are Standard Timber Purlins also Thermal Breaks?

Postby JK_Rameka » Wed Dec 20, 2017 2:13 pm

Hi Albrecht,

Can you confirm if standard fixed timber purlins fixed horizontally and perpendicular to steel rafters can be treated and added into the roof calculation as thermal breaks?
Does the 35mmm & 45mm timber thermal break option include this orientation of purlin above the rafter, or is it assigned only to the situations where these timber packers are fixed along the top of the steel rafters just the same as how you would install other thermal breaks?

My gut feeling is that the 35mmm & 45mm timber thermal break is an "extra" to the calculation and not the actual purlin itself, which is probably accounted for elsewhere in the calculation. Otherwise if this was the case then all purlins would be able to be accounted for in the thermal break section of the calculation.

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Re: Are Standard Timber Purlins also Thermal Breaks?

Postby Albrecht Stoecklein » Wed Dec 20, 2017 2:37 pm

Hi JK,

If the timber battens are along rather than perpendicular to the steeel framing they can be considered as thermal breaks. If they are mounted perpendicular the area that they cover under the steel framing is so small that they would have to be ignored. Purlins are normally mounted perpendicular to the framing and are therefore usually not accounted for the R-value calculations.

In terms of the placement: For roofs it is much more effective to have any thermal break under the framing rather than above the framing. Heat will simply bypass any thermal break that is above the framing and be lost into the cold air cavity between the insulation and the roofing. I would even go so far as to say that a thermal break above the steel framing is pointless and should be ignored in any R-value calculations.

I hope that helps.

Sunny regards

Albrecht Stoecklein
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Joined: Sat Jun 13, 2009 5:30 pm

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