Timber frame build in Ireland

[CKelly]

Hi, I am Caroline living in Co. Clare and building a one bed timber frame house for myself in my mother's garden. It is being built by a neighbour who is a carpenter and my son was helping him at the beginning. The frame is up, walls of OSB and insulation and outer membrane and batons on the roof. I have joined this forum because I have a cladding dilemma, and was interested in what ProDave was doing on his Scottish timber frame house. We started out with a concept and a design for planning permission, but as we go along everything is changing as decisions are being made due to circumstances, money etc. 

[CKelly]

To follow on from my introduction - the planners stipulated that the house should be rendered to match my mothers block built bungalow, so far we have decided to put insulation externally as well as internally in the stud walls. So is the only way to clad the house to match a block built house, is to use cement board and plaster/render it? Part of me is rebellious and wants a timber house to look like a timber house and clad it in wood (the cheaper option), it seems. 

[nod]

You can render directly onto the insulation 

[ProDave]

I have render direct onto wood fibre external insulation. It's not cement render but one of the "thin coat" render systems designed for such.

[Conor]

10 hours ago, CKelly said:

To follow on from my introduction - the planners stipulated that the house should be rendered to match my mothers block built bungalow, so far we have decided to put insulation externally as well as internally in the stud walls. So is the only way to clad the house to match a block built house, is to use cement board and plaster/render it? Part of me is rebellious and wants a timber house to look like a timber house and clad it in wood (the cheaper option), it seems. 

 

No, you can just use K-rend directly on to the insulation, that's what we are doing. Plus you'll never need to paint your house.

 

Where abouts in Clare are you?

[ADLIan]

It is not recommended or accepted good practice to render directly to timber frame or onto insulation on timber frame. Render should be onto a render carrier board with a vented and drained cavity.

[CKelly]

The way we are doing the walls is a timber stud wall, with OSB on the outside, which has been done, then Xtratherm 40mm insulation board, membrane and batterns, air gap and then Cladding. Internally there will be rockwool and then planking. What would people recommend as a cheap easy system for making the house look like its been made of Block and render? 

We have only the OSB on so far so there is flexibility to change materials at present. I was happy to put the Xrtatherm board on the outside, but cannot see how once can render straight onto that. Is cement board the only way? I have many tubs of lime putty I made from building lime kilns and burning lime, a few years ago that I would love to use either as a whitewash or make a lime render, but fear it will flake off after a short while. 

 

[CKelly]

On 25/07/2020 at 08:14, Conor said:

 

No, you can just use K-rend directly on to the insulation, that's what we are doing. Plus you'll never need to paint your house.

 

Where abouts in Clare are you?

What insulation are you K-Rending onto? I am in Whitegate, and used to live in Holywood many years ago. 

[CKelly]

On 25/07/2020 at 12:27, ADLIan said:

It is not recommended or accepted good practice to render directly to timber frame or onto insulation on timber frame. Render should be onto a render carrier board with a vented and drained cavity.

 

That was our original plan but it looks expensive, board, and then render. What carrier board would you recommend? And could a plasterer who usually does block built houses use the same plaster/cement based mix for board on a timber frame or will there be movement and cracking?

[CKelly]

On 24/07/2020 at 22:06, ProDave said:

I have render direct onto wood fibre external insulation. It's not cement render but one of the "thin coat" render systems designed for such.

I have followed your blog about how you did this a few years ago, how has it weathered? Would you recommend it again? where does the air gap go between the wood fibre and the stud wall?

[Conor]

45 minutes ago, CKelly said:

What insulation are you K-Rending onto? I am in Whitegate, and used to live in Holywood many years ago. 

My partner is from Parteen and we holiday in Kilkee a fair bit.

 

We'll be rendering on to EPS.

 

[CKelly]

The plan for the walls is from the inside to outside, airtight membrane, rockwool, OSB, 40mm Xrta therm, watertight membrane, battens, airgap and cladding. Another timber frame  builder has warned me that putting 40mm Xtratherm foil backed polyurethane board on the outside of the OSB, could cause a dew point between the OSB and the foil. Inside the insulation is going to be rockwool or similar in the stud walls. Has anyone encountered this? 

[A_L]

@CKelly, your build-up is potentially troublesome in the way described, foil faced Xtratherm is an effective vapour barrier

 

1) is the internal airtight membrane also a vapour barrier

2) how thick is the rockwool

3) is the foil on the warm side of the Xtratherm

4) is the watertight membrane water vapour open but liquid water proof

 

 

[CKelly]

Rockwool is 140mm thick, foil is on both sides of the Xtra therm which is Safe-R Framing Board SR/FB is designed for use with steel or timber frame applications up to 18m in height. With a Euroclass B Fire Classification the framing board can be used between studs or as an insulated sheathing board. Using SR/FB provides excellent U-Values and improved thermal bridging detailing.

Instructions from Xtratherm say

When using SR/FB as a sheathing board, fix the insulation outside of any breather membrane or timber sheathing on the external surface (a second breather membrane may be added at this point for further protection) and temporarily fix with large headed clout nails. Ensure boards are closely butted and stagger jointed. 4. Place a sealed vapour control layer of polythene with lapped and sealed joints over the internal stud face. 5. Install cavity barriers into the cavity as required under building regulations. 6. Apply the internal finish as normal using fixings as recommended by timber frame supplier.

[A_L]

1 hour ago, CKelly said:

Place a sealed vapour control layer of polythene with lapped and sealed joints over the internal stud face.

 

As long as this layer remains effective the wall will work but without it interstitial condensation will occur. Personally I would not want to depend on it. Putting the Phenolic board inside he Rockwool and moving the OSB to the inside of the studs would be the easiest solution

[dpmiller]

no service void on the inside will be a pain.