Making buildings airtight is key to keeping them energy efficient. If you are attempting to reach PassivHaus standard you will need to reduce air leakage to 0.6 ACH (Air changes per hour) but if you're not, 1.5 ACH a reasonable target (this is significantly better than the Building Regulations requirement; sadly most new buildings still only achieve around 4 or 5 ACH).

Making your building airtight is also important because you need to stop warm humid air from seeping through the insulation of the building, and forming condensation within the timber walls.

The WikiHouse blocks may allow air flow through tiny gaps between the cassettes. It is therefore really important to properly wrap and line the chassis to keep it as airtight as possible. There are a few options on how to do this:

VCL membrane and tape  

The Vapour Control Layer acts as a barrier to stop warm, moist air from the inside of your space from entering the wall build-up, hitting the cold outer area of the wall and causing condensation (damp). 

We suggest specifying a Vapour Control product from known manufacturers such as Pro Clima, Sarnafil, Glidevale… These manufacturers can be contacted and consulted to check the most suitable product(s) for your design.

The VCL can be installed on site. You’ll need to fix the membrane to the WikiHouse chassis as per the membrane manufacturer’s installation instructions, checking if you need to overlap the sheets and adequately sealing penetrations and joins. The VCL can be cut to fit over internal ribs and services in the WikiHouse structure, then thoroughly sealed around these penetrations in the layer.

Make sure to specify where possible using one company’s product suite, getting their specification advice ahead of time. Check for a system warranty, rather than a product warranty. That way, any issues with the performance of the VCL can be clearly addressed by the manufacturer. 

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Liquid applied 

There are a number of liquid applied VCLs on the market, such as Blowerproof and Passivepurple.

This can be applied to the inner face of blocks off-site, then reapplied over joins between blocks once the chassis is assembled. Alternatively, it could be applied once the chassis is in place, coating the entire internal surface of the cassettes. 

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Lining boards

For the small number of projects with a lesser requirement for airtightness values, there are some boards on the market with an integrated vapour barrier that could be used as a really simple way to line out your chassis whilst preventing too much moisture from reaching the internal wall build-up. Always consult the manufacturer to check if the product is appropriate for your design. Vapour panel example here.

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Build tight, ventilate right.

With the building now airtight, it becomes necessary to properly ventilate the building so there is a constant supply of fresh air into the building and stale, humid air is removed, but without losing any of the warmth. The best solution to this is to use MVHR (Mechanical Ventilation with Heat Recovery) with a 'Full summer bypass' mode. (See Principles of good design - Designing for MVHR for more information).

Finishes for walls / ceilings

The WikiHouse chassis has internal ribs that create a clear service zone. Your internal linings will go over these ribs. Depending on your material choice, you will likely be fixing your linings into the timber ribs, or you could fix battens over the ribs to give further flexibility.

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Some alternative ideas for internal linings

• Cork board with/without lime render, depends if a smooth finish is desired.
• Wood fibre panels - Good for acoustic dampening in spaces. Makes a nice ceiling lining.
• Plywood - unstamped and a higher grade for finer finish quality. You may need to fire treat it if it’s a large area of exposed timber.

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Finally… plasterboard.

The most conventional approach is to fix plasterboard panels onto the chassis. These serve the dual purpose both of providing the requisite fire protection and adding some additional thermal mass to the space.

Use tapered-edge panels that are 1200mm wide, as these will align with the protruding 'ribs' of the structure.

Because the chassis is so straight, no skim is required. Mesh tape and fill is fine.

Finishes for floors

You can lay a flooring material of your choosing over the WikiHouse floor block. Consider using soft floor materials when more sound deadening is required, e.g. at first floor.  

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