Project specification
Insulation Strategy
Walls
The rear external wall and kitchen extension will be externally insulated using 100mm phenolic foam to achieve a U value of 0.2 W/m2K.
To maintain the external façade, the front external wall will be insulated internally with phenolic foam dry-lining board (75mm) to achieve a U value of 0.30 W/m2K. The existing plaster will be removed and a parge coat applied to the exposed brick work. This will ensure an even surface to fix the thermal boarding to and should assist us in improving the air-tightness of the house.
We had hoped to externally clad the side passageway, but the loss in width would not have been acceptable as this is the main access route for a number of other dwellings. The strategy will now be to insulate internally with phenolic foam dry-lining board or, where space is limited, with Spacetherm insulation boarding. Where we can, we will aim to achieve a U value of 0.30W/m2K.
To compensate for the loss of valuable floor space due to this measure we will be removing the chimney breast in the front lounge.
Roof
The roof above the attic conversion is to be replaced using a breathable roofing membrane. This will enable us to use an unventilated roof construction and therefore the full depth of the rafter (100mm) can be used for insulation. To achieve a U value of 0.10W/m2K, we will be fixing a further 100mm of rigid insulation boarding below the rafters. This strategy will also be used for the kitchen extension roof.
Ground floor
The front of the building has a suspended timber floor. This will be insulated from below with PIR insulation board (150mm) to achieve a U value of 0.22W/m2K. To improve air-tightness the existing floorboards will be replaced with a chipboard floor.
Cellar
The underside of the ground floor stairs within the cellar are to be insulated with phenolic foam boarding. The wall under the stairs at ground floor level will be replaced with a timber stud wall with the studs in-filled with rigid phenolic insulation boarding.
Windows and doors
The windows we will be specifying are argon filled triple glazed timber units (FSC certified) with a whole window U value of 0.9W/m2K. The windows have soft low-emissivity coatings to give an optimum balance of heat loss and solar gain. The front and back external doors will be replaced with a thermally insulated timber doors with an overall U value of 1.2 W/m2K.
Roof Windows
The old roof windows will be replaced with new Velux windows with a whole window U value of 1.4 W/m2K.
Cold Bridging
To minimise thermal cold bridging problems at wall junctions we will carry out the following:
Where dry lining is proposed:-
- All window and door reveals to be insulated
- Dry lining will be returned by 600mm on internal walls
- Ensure insulation continues through all floor voids
Where external insulation is proposed:-
- Insulation to continue 200mm below assumed floor insulation
Heating Strategy
The house is presently heated using an old gas back boiler that is very inefficient. This also supplies hot water for the kitchen and bathroom except for the shower which is electric. There are also a couple of standard gas fires in the two reception rooms, which are used for supplementary heating.
We propose to remove the gas back boiler and replace it with an ‘A’ rated gas condensing combination boiler. A passive flue gas recovery unit called a GasSaver will be installed to improve the overall efficiency. This works by absorbing the latent heat of the condensing flue gases, which is then used to preheat water used to supply domestic hot water.
A solar hot water system is to be fitted to supply free hot water during the summer months. The system has been designed for use with combination boilers and includes a pre-heat solar thermal store. The flat plate collector will be located on the front southwest facing roof.
The tenants are keen to retain some form of secondary heating and therefore we will be replacing the gas fire in the main living area with a small wood burning stove. The other gas fire will be removed.
The heating system will be a controlled by a new innovative heating controller called a Wattbox. The Wattbox learns the behaviour patterns and temperature preferences of household occupants and uses this to control household heating.
Lighting and Appliances Strategy
The property is to be re-wired and therefore we will ensure that all fixed lights are fitted with dedicated energy efficient light fittings.
All white goods (fridge, freezer, washing machine and dishwasher) will be replaced with A++ rated appliances.
