Gutex Multitherm Roof Insulation - Passive House Insulation Series (part 3)

Niall Crosson, our technical manager, describes the benefits of applying Gutex woodfibre board to the outside of a pitched roof. He outlines the key steps to applying Gutex Multitherm wood fibre insulation to the roof of his new build Passive House. The video explains the use of Heco screws and the application of Solitex Plus Connect, a windtight roof lining breather membrane that features an integrated windtight tape.

[@siriosstar4789]

i went for the open rafter bay look by installing T&G wood panels on top of the rafters which makes a nice looking ceiling inside .however , i had to double up on the insulation panels in order to achieve a respectable level of roof insulation .

[@FiscalWoofer]

Just love this short video...referenced it soooooo many times! Thank you guys!

[@EcologicalBuildingSystems]

Thank you. So pleased to hear it has been useful!

[@janisskists4106]

nice&clear

[@EcologicalBuildingSystems]

Thank you! Cheers!

[@zororat]

I like the idea that it looks more structural than conventional insulation board, I also think the demonstration of the screw method is fantastic to prevent shearing, I wish I'd seen this before, I imagine there's lots of warm roofs installed not bothering to use this method. Unfortunately I'm a bit put off by the fact this material looks just like MDF and gives me the fear it will soak up moisture like a sponge and swell like crazy. I hope to be proven wrong though, but is there a demonstration of it being exposed to water?

[@EcologicalBuildingSystems]

Hi Michael Gutex boards have been used since 1932 and all external boards are hydrophobic, treated with Parafin, and do not absorb water. Additionally they will be protected by a Solitex Plus windtight breather membrane :-) This blog may help: foursevenfive.com/blog/nature-does-it-best-gutex-wood-fiberboard-insulation/

[@zororat]

@@EcologicalBuildingSystems thank you for the response, I'll have a read, is the treatment throughout the board, in other words, when cut, does the new cut edge of the board still repel water

[@ArthurDentZaphodBeeb]

Excellent explanation. Just wish you'd have longer videos to show more installation techniques. How are you maintaining your continuous air barrier?

[@EcologicalBuildingSystems]

Thanks, we have much longer installation videos on our you tube channel.

[@pcatful]

1. I see no structural shear sheathing in your assembly. 2. Moisture might travel up to the cold side of the insulation and condense. A moisture barrier (on shear sheathing below) and/or closed cell foam roof top insulation prevents that. The air layer you seem to be building in below the roofing material is helpful but can it stop condensation?

[@EcologicalBuildingSystems]

1. No internal Shear panel is needed on the roof as it is a cut roof supported by engineered glulam beam tied to timberframe walls which have shear panels fitted inside (all certified and inspected by structural engineer). 2. Airtightness and vapour control layer INTELLO PLUS membrane is fitted inside. Blown woodfibre between rafters. 80mm Gutex outside. Vapour resistance inside is 60 times more vapour resistant compared to outside (i.e. Sd 14m inside compared to 0.24m outside). Above the Gutex is a vented cavity. This is a highly breathable and moisture safe specification with extremely high levels of safety minimising interstitial condensation risk

[@g4egk]

I don't know how else you'd fasten it but do the long screws cause a problem with thermal bridging? Or is it minimised as they are embedded in the rafter?

[@EcologicalBuildingSystems]

The size and quantity of screws is optimised to balance the thermal and structural performance. The screws are fixed into the battens at about 750mm centres and there are only as many screws as needed based on a HECO screw calculation which Niall carried out. The rafters/studs are 225mm thick and embedment is a min of 40mm so there is an additional 180mm timber behind every fixing which will help offset these limited point thermal bridges. There is also a 50mm insulated service cavity on the interior side too which further reduces the effect. Therefore, in this build up with these fixings the thermal bridging is insignificant.

[@natureplusscienceequalsjoy6656]

@Ecological Building Systems Will this work with Rockwool Super, even though it is not interlocking? I have limited options available in my country and would prefer to add insulation to the roof over the rafters rather than on the inside of my already small house.

[@EcologicalBuildingSystems]

Hi, I’m afraid we can’t provide guidance with other products such as Rockwool Super. I’d recommend to contact the manufacturer directly for more information.

[@mercedesslr722]

Thank you for the video. Question, why have you decided to go with Multitherm + Membrane and not just Ultratherm without membrane?

[@niallcrosson5859]

Hi Konrad. Mulitherm has a lower conductivity and cost. Also, I would have had to prime and tape butt joints in ULTRATHERM. Therefore for performance, robustness and cost efficiency I used this spec.

[@EcologicalBuildingSystems]

thank you

[@kermitefrog64]

But who do you purchase this product from in the United States? This looks like a great product but this is not going to be available at Lowes or Home Depot. They have run out most of the Lumber Yards.

[@EcologicalBuildingSystems]

For USA, please contact 475 Building Supply for Pro Clima airtightness and wood fibre insulation. 475.supply/

[@danielamoebius2558]

What do you do about roof overhangs?

[@EcologicalBuildingSystems]

Hi Daniela, Based on local planning requirements this house was based on the vernacular architecture of the region where Irish farmhouses dominate the area. These buildings are built with flush gables and no soffits/overhangs. This building ties in with that. To address weathering/potential overheating risk on glazed areas, exterior shading is provided via canopies/brie soleil etc.

[@redsresearch]

how does tht reduce the shear load

[@EcologicalBuildingSystems]

A calculation is carried out to know exactly how many shear and suction screws are required to secure the wood fibre and roof build-up.