Insulation and cladding

[colinb4987]

So I've landed myself the job of insulating the sides of our house. Thanks to a wide variety of factors, there is no option to pay someone to do it.

XPS will be in the ground and rise 300mm up the walls. From there to the underside of the eaves is approx 5m. Eaves overhang 300mm plus gutters.

We have surplus wool and wood fibre insulation in batts, so those are the materials we will use.

The whole lot will be clad in 20mm thick cork panels, which are 500x1000mm as supplied. They can be screwed onto a substrate, or glued (if the whole surface is used).

My basic idea was to

• make or buy 200mm deep I-section columns from timber and OSB
• Fix into the brick with concrete screws (or plugs and screws) at 500mm spacings to form a series of vertical channels, 500mm wide.
• Fill channel with insulation, screw cork onto outside face.
• Lay cork stretcher bond with thin bead of adhesive between boards (not needed according to manufacturer but I don't want to risk water ingress)

Aside from detailing around windows and corners (which will no doubt be a faff), are there any obvious flaws to this approach? Any advice on improving it (making it easier to install or less error prone), or any proposals for alternatives?

 

[XTiffy]

I can't comment on the overall approach, technique and materials you are using. However to me you are over complicating the job with your I-Beams.
What you are producing is an OSB boarded wall, spaced off of the wall, with the I-Beam forming a space for you insulation.
Why do you not just batten the wall at your chosen spacing, fix the OSB in sheets (crosscut horizontal at 1200mm, if you want to make them easier to handle). Then apply your "spacers" on top, to suit thickness of insulation, these again could be more than one batten to achieve the desired space.
No routing etc. needed!

 

[Inspector]

I can't comment on the overall approach, technique and materials you are using. However to me you are over complicating the job with your I-Beams.
What you are producing is an OSB boarded wall, spaced off of the wall, with the I-Beam forming a space for you insulation.
Why do you not just batten the wall at your chosen spacing, fix the OSB in sheets (crosscut horizontal at 1200mm, if you want to make them easier to handle). Then apply your "spacers" on top, to suit thickness of insulation, these again could be more than one batten to achieve the desired space.
No routing etc. needed!

You misunderstand. He is using I Joists, purchased or home made of solid flanges and OSB webs, to make a cork sheathed wall. Basically wrapping the brick building to insulate it. Using the I Joists provides a thick insulated wall with very little heat/cold transfer compared to solid 2x wood because of the thin OSB webs. Theoretically more energy efficient.

Colin one issue you haven't addressed is the moisture (vapour) from inside the building moving through the bricks will get trapped in the insulation. It eventually may lead to rot and or mould problems. If it is a vented double brick wall moisture should be able to get out but if it is single brick you will have a problem. Venting your wall is going to be problematic.

Pete

 

[XTiffy]

Though I now understand that the space you are filling with insulation is 200mm, I still beleive there are easier ways of achieving this. ie. Vertical battening the wall and screwing the OSB to the side of the battens. Then attach battens to the front edge of the OSB (glue and screw) to form the fixing surface on both sides if you wanted a wider fixing surface.
I also believe (as Inspector points out) you need to think about moisture barrier.

 

[Jones]

Screw 2x2 to the wall then screw osb spacers (4-500mm long) to that then screw 2x3 to that. This will allow you to correct any straightness as you go and lengths can join at the osb. On the insulation front normally external wall insulation is only 100 mm thick as is cavity insulation so you might be putting in more than necessary. Rockwool EWI comes as stiff batts which are screwed to the wall with tube spacers and big plastic washers. That is then rendered over with a reinforcing mesh in the render. To prevent slumping it might be worthwhile getting some of those fixings. XPS is not suitable for ground contact it is not waterproof and will get saturated and wick moisture. For ground contact you need EPS ,extruded polystyrene, it's much more expensive. Generally though the EWI does not go below dpc level,if you do then incorporate a dpc. I have never seen cork batts used externally,are you sure they're suitable? If they're valuable it might be better to sell them and buy some other kind of cladding, you don't need the extra insulation. With many claddings you would want a breather membrane.It's worth having a think about water vapour, dew point etc, you may need an architects advice.

 

[Jones]

You'll find a lot of good advice on the Centre for alternative technology website. It's worth a visit if you're ever close by and they've a good bookshop too.

 

[HOJ]

I won't comment on your proposed insulation method, I would suggest that needs more consideration, as has been said before, but with regards the I joist, the drawing I have shown below is the construction principal for a system I have used when building TF houses that have full fill EPS bead insulation pumped in once its is built, the frames are 3" X 2" regularised, treated, C24 and the gussets are 9mm thick X 150mm tall X depth required, nailed on with ring shank nails.

 

[Hornbeam]

There are a number of commercial spacer bracket and bar systems which you coulduse such as ashgrid. As said by inspector you need to allow for any moisture movement so you will need a vapour control layer (breathable but waterproof and then a vented cavity outside that of around 25mm minimum,
Normal approach would be to cross batten but you need the outer battens running vertically to allow air to enter the cavity and vent out at the top. This would mean your I beams need to run horrizontally which would compromise their strength

 

[Inspector]

Horny. In that instance you would run the I beams vertically, cross batten and then an additional set vertically. The air can travel up and down and even side to side around windows if it feels like it. More work and materials though. In the end you are almost framing up a new house and the economics may not add up. Plus it is a bucket load of work.

Pete

 

[colinb4987]

Thanks for the input so far. Briefly, as on mobile at the moment:

Moisture management is dealt with - full analysis complete, no risk of interstitial condensation given the rest of the buildup of the wall. Additional ventilation/cavities etc. not needed.

Insulation thickness is actually less than I'd like, but I don't want to go too close to the edge of the eaves.

Insulation materials have their rationales as well, selected with specialist guidance

Cork cladding (MD Facade) is specifically suitable for this external use

@Jones you're basically suggesting C-beams rather than I beams, right? I like, not least as it does away with the faffery of routing slots, and th OSB webs can be nailed to the timbers rather than messing with glues or screws

 

[Jameshow]

Thanks for the input so far. Briefly, as on mobile at the moment:

Moisture management is dealt with - full analysis complete, no risk of interstitial condensation given the rest of the buildup of the wall. Additional ventilation/cavities etc. not needed.

Insulation thickness is actually less than I'd like, but I don't want to go too close to the edge of the eaves.

Insulation materials have their rationales as well, selected with specialist guidance

Cork cladding (MD Facade) is specifically suitable for this external use

@Jones you're basically suggesting C-beams rather than I beams, right? I like, not least as it does away with the faffery of routing slots, and th OSB webs can be nailed to the timbers rather than messing with glues or screws

If insulation isn't as thick as you would like could you upgrade to celotex/kingspan?
Better thermally and from a damp perspective?

 

[Jones]

Good that you've done moisture plan and chosen insulation, it sounded a bit as if you were using some leftovers.
Yes I was suggesting a c beam, a Larsen beam is another option, that is a ladder like beam with 8-12" rungs of OSB at 4-6' centres. Easier to make than a continuous slot for an I beam and invented for this insulation application.