Anne Thorne Architects – Site Diary Week 4
Air-tight membrane being installed to upper floor ceiling. Being brought down the side of existing partitions, and over the top on new ones.
Sandwood are taking extra-special care in sealing the membrane into the existing wall plaster, and taping every join seamlessly.
An interesting on-site belt and braces approach to the the junction with the front wall that Sandwood have built on site is the double-sealing of the ceiling membrane to the plaster behind the internally insulated external wall, and the wall air-barrier we are installing on the internal side of the sheepswool filled timber battens.
This helps ensure continuity of the air-tight barrier between the party and external walls.
An issue arose with the specified manufacturer’s installation guidelines for the wood-fibre boards to the party walls (these prevent our house heating their neighbours, keeping our heat for our house).
Some wood-fibre board suppliers require you to use a proprietary plaster system (5 times more expensive than gypsum plaster…). We instead sourced a wood-fibre board supplier that would guarantee using normal lime plasters.
To install the boards on the existing plastered walls, a scratch-coat of lime hemp plaster is applied, then a coat of the lime hemp plaster is applied to the entire surface of the wood-fibre boards, to ensure there are no air gaps. This layer bonds the boards to the wall, along with additional plastic fixings. The boards are then finished is a pre-mixed fat lime plaster.
This creates a breathing construction that will help to regulate internal air moisture in the house.
We’ve also decided on site to extend the internal lining to the kitchen walls where the kitchen units are to go, so that we do not need to puncture the internal wall plaster to the externally insulated rear walls, which we are depending on for our air-tightness. We originally only battened out one wall for services. 2 walls still remain solid do provide an element of thermal mass to the room.