Welcome to the blog for the retrofit of a pair of semi-detached houses on the Hawtonville estate, in Newark on Trent, Nottinghamshire. The retrofit is a partnership project between Hockerton Housing Project (HHP), consultants and lead contractors, and Newark and Sherwood Homes (NSH) the Arms Length Management Organisation (ALMO) for Newark and Sherwood District Council, and the social landlord for the properties.
The retrofit project is being funded under the Technology Strategy Board’s Retrofit for the Future Competition, aimed at finding innovative ways to dramatically improve the energy efficiency of existing housing.
The blog will be updated regularly with reports, photographs and videos documenting progress of the retrofit project.
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What is the estimated cost of retrofitting one house and what would be the pay back time in years based on reduced fuel bills?
Hi Dave
The budget for the two houses is £150k, so significant cost per house. It is a demonstration project however so has a lot of associated costs that would not otherwise be incurred. Even so, still costly as a one-off, but the idea of the competition is to trial solutions, monitor them for 2 years, and see which really work; information that is sadly lacking in this arena at the moment. If it works and was scaled up for hundreds of houses then costs would drop significantly.
You may be interested in the new coalition government’s “Green Deal’ proposal to fund retrofit of existing houses. The basic concept is that retrofit work requires no up-front funding from the homeowner, and is paid back over time (20-25yrs) via a “charge” on their energy bill; the charge will be less than the savings made as a result of the retrofit work, so the net energy bill will still be less than is currently being paid. If you move house the charge remains with the property, not you, as the new owner/tenant is then benefitting from much lower bills as a result of the work.
So, how is progress???
How does the external insulation ventilate behind the outer brick leaf? If it doesn’t are you worried abou damp?
Lastly, how is the outer brick leaf tied back to the existing structure for support?
The cavity between the new external wall and the original wall is fully filled with dritherm insulation; there is no clear gap in the cavity.
A gap in the cavity is a measure sometimes used with the idea that wind driven rain can penetrate the external brickwork and therefore conduct moisture into the cavity. The clear space is supposed to allow this moisture to run down the internal face of the external brick work and not come into contact with the cavity insulation. This could be a problem with a very porous brick and porous mortar. We use only bricks with a very high level of frost resistance which are also very water resistant, standard mortars [also water resistant] and fully fill all perps. It is not necessary for the insulation in the cavity to have any ventilation at all. The insulation is not hydroscopic so will not transfer moisture. The insulation has a water resistant coating on both faces. We use 3 vertical layers of the insulation thereby providing 6 water resistant layers between the inner and outer skin of the building. Any ventilation [air movement] within the cavity can and will affect the performance of the insulation. Fully filled cavities using compressible/flexible insulation is the best way to achieve high performance in cavity wall insulation. [You probably will have realised that we do not subscribe to the idea of breathing walls!]
The new external skin is attached to the original internal wall using Teplo wall ties. These look a little like a thin round file. A hole was drilled into the original wall and filled with cement grout using a grout gun. The tie was hammered into the hole and held in position by the grout. The external wall is then built up in the normal way incorporating the wall tie. This method was tested for strength by the manufacurers of the tie and found to be satisfactory.