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The A 100 House

I am currently involved with the construction of a house with what is promising to have a SAP of A 100!

To those of you who do not totally understand the why's and wherefores of this, in its basic form, on paper this house will be just about as energy efficient as it can get.

The construction will be timber frame, conceived and constructed by MBC, with a brick external skin and tiled roof, so will from the outside will look just the same as most other houses in the road.

Of course this is where the comparison ends, as the structure is super insulated and airtight, built on a ground bearing passive standard floor slab, also using very high performing windows and doors.

Working alongside the Architects and Timber Frame Company, my role is that of Project Manager employed by the client, providing certain design input and my usual Pre-Construction works. This will lead on to the Construction Phase where we will be employing the relevant Sub-Contractors to complete the build.

On site works have only just commenced with the demolition of the existing house, moving on to the groundworks by the end of July. The Timber Frame Company, who also construct the floor slab as part of their brief, are due to arrive mid-August.

I have decided to update this article in each of my Newsletters in the form of a blog, until its completion, therefore keeping you informed of the progress during the construction of this exciting project.

Addendum, 26th October 2015 - Following on from this article last time;

Since there is no traditional strip foundation, the ground over the footprint of the new build has to be reduced and carted away down to a decent sub-ground strata, in this case by about 750mm.

This area is then filled with consolidated crushed hardcore to provide a solid "mat" for the passive slab to be constructed on.

The slab is formed with several thicknesses of ExPS (Extruded Polystyrene) formers which apart from providing the shuttering for the reinforced concrete, deliver all the thermal performance measures to create a "passive slab"

Whilst in theory, there should be little use for heating requirements, underfloor heating pipes are incorporated within the slab which once power-floated becomes the structural finished floor.

All foul drainage has to be installed before the slab is created so at time of writing this, all drainage, services etc are in place with the passive slab cast, and is awaiting the arrival of the timber frame.

Since the last time;

Timber frame is now erected with windows installed, roof coverings well under way and the brick skin making good progress.

We are using a recently developed "twin wall" system by MBC which is in effect two open panel frames fixed back to back forming a 300mm hollow frame that is then sealed each side and pumped full of insulation. Not only does this design give an impressive uValue and lack of cold bridging, but equally important an extremely notable airtightness envelope. On this build airtightness is quoted at 0.6 whereas a decently constructed building would usually be considered better than respectable at 3.0 and to satisfy Building Regs even higher (up to 10.0).

It is therefore extremely important to consider this requirement when designing in any penetrations through the superstructure. Even a simple item such as pipework for an outside tap or cables through the fabric for lighting has to be carefully designed and incorporated with your average contractor not always understanding the implications.

The sealing of window frames to the timber frame is carefully designed with Velux roof lights requiring thermal collars to avoid cold bridging.

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