Wattbox heating control up and running!

For the project we specified a proprietary insulation cladding system supplied by Weber. The system is a render protected based on phenolic foam with a meshcloth reinforced render and textured synthetic finish. With 100mm phenolic foam insulation the calculated U value of the back wall should be around 0.18 W/m2K - that's over a tenfold improvement on its current thermal performance. Fisrt the phenolic insulation board is cut and mechanically fixed to the existing masonary substrate using special fixings.

The new windows were bought forward so they were flush with the exisitng wall. This detail eliminates the need to insulate the window reveals which can be problematic where the windows are set back into the wall and also helps to reduces cold bridging.

Once the insualtion is fixed a 6mm meshcloth reinforced render is then applied. This provides weather and impact protection.

Once the undercoat is dry the final finish can be applied. The textured finish is tinted to the required colour.

The heating strategy for the project was to replace the inefficient gas back boiler (located in the rear lounge) with a new modern ‘A’ rated gas condensing boiler. The old system used a regular boiler with a hot water cylinder located on the first floor and the cold water cistern located on the top floor attic conversion. For the project we decided to replace the regular boiler with an ‘A’ rated condensing combination boiler. We also wanted to include a solar hot water system into the specification. This can be difficult with combination boilers as most do not accept pre-heated hot water. We decided to specify a heating packaged system by UK based Alpha Boilers that has been developed to work specifically with a combination boiler called SolarSmart. The most logical place to locate the heating plant was on the party wall in the top floor toilet. The original plan was to retain the toilet facility by moving the toilet and wash basin onto the bedroom partition wall. When the plant had been installed we realised that we had no option but to increase the size of the room by moving the partition wall forward onto the landing.

Unlike most conventional solar hot water systems the SolarSmart heating package developed by Alpha Boilers has been designed for use with combi-boilers. The package consists of a flat plate solar collector, a 90 litre unvented cylinder store (smaller and lighter than most solar cylinders thereby minimising the amount of space required) and a solar valve developed by Alpha that enables it to operate with a combination boiler. The system is a drain back rather than the more common pressurised system. A drainback system uses a pump to circulate water in the collector from a drainback vessel. If there is heat to collect from the collector the pump is activated and the water is pumped to the collector and then through a heat exchanger. When the pump switches off (for example at night) the fluid flows backwards under gravity, refilling the drainback vessel. This arrangement protects the solar fluid from temperature extremes that can occur in winter and in summer. As water is used as the heat transfer fluid it should not need changing unlike pressurised systems that use antifreeze.

The Gassaver is an innovative energy saving device that sits between a combi-boiler and flue. It works by storing the condensate normally expelled into the atmosphere via the flue and then uses this to pre-heat the cold water entering the boiler. In independent tests the device can save between 37 and 50 per cent of the gas used to heat hot water annually, depending on the efficiency of the boiler. Another advantage of the product is that it requires zero maintenance (it has no controls or moving parts). The product was developed by the British company Zenex Energy and the technology is now sold by a number of boiler manufacturers (Alpha and Baxi).

The image shows the 90 litre solar cylinder (unvented) and to the left the drainback unit. The solar cylinder is light enough to be wall hung. The manifold and circulation pump are factory fitted to ease installation.

To fit the heating plant in the top floor bathroom we had increase the room size by moving the partition wall forward.

The original plan was to remove the chimney breasts from both reception rooms to free up valuable living space (and to replace that lost due to the dry lining). However, during the design stage of the project, the tenants expressed a wish to retain some kind of focal point in the main living room such as a gas fire. We therefore decided, with agreement from the tenants, to retain the chimney breast and replace the inefficient open front gas fire with a small wood burning stove.

The preparation work required for this was relatively straightforward. The main construction work involved opening up the existing chimney to meet the dimensions required to accommodate the new stove. The original hearth had been removed so a new one had to be built out of slate. To reduce heat losses the chimney breast and the back of the new opening were dry lined with Kingspan K17 thermal board.

The wood burning stove was supplied and fitted by local specialist company Hagley Stoves. From the tenants perspective it was important that the stove specified was easy to operate and maintain. We also wanted to keep the heat output on the low side to minimise over heating problems. The appliances also had to be an exempt appliance as the property is in a smoke control zone. Hagley Stoves recommended a Handol 52 cast iron stove manufactured by NIBE based in Sweden. The stove has a heat output of between 3kW - 7kW and operates with a burn efficiency of 79%.

The design specification for the attic roof was to insulate to achieve a U value of 0.12 W/m2K. To achieve this we proposed to insulate between and under the roof rafters utilising the full depth of the rafters (as the roof was re-tiled we were able to specify a breathable sarking membrane removing the necessity to provide a 50mm ventilated cavity below the sarking). This was achieved using 100mm of phenolic insulation (Kingspan K7 board) between the rafters and 92.5mm Kingspan K17 insulated dry lining board under the rafters (80mm phenolic insulation board plus 12.5mm plasterboard). To hit the 100mm we had to fix counter battens to most of the rafters to extend their depth. Unfortunately, additional roof rafters had been fitted alongside the original rafters (probably when the loft was converted in the 1980s.) These caused lots of problems when it came to cutting and fitting the insulation as can be seen in the image above.

The old velux windows in both attic bedrooms and landing have been replaced (new U value 1.4W/m2K). To reduce cold bridging and heat loss between the window frame and roof structure a Velux insulation collar was fitted. The underfelt collar can be seen in the image above. Note also the Kinspan K17 insulation board fixed under the roof rafters

The image above shows the Kingspan thermal board fitted prior to a plaster skim being applied. To minimise the risk of interstitial condensation occuring it is important to include a vapour control layer on the warm side of the insulation. A benefit of using Kingspan K17 is that the vapour control layer is built into the product.

The ground floor at the front of the property is suspended timber and un-insulated. The property also suffers considerable heat loss as a result of air leakage between the old floorboards.

The back lounge ground floor is concrete slab and is not insulated. The back lounge is directly above a brick vaulted room in the cellar as shown above. Our original design was to excavate the existing floor and add insulation (60mm) below a new concrete slab. This was preferable to insulating above the existing slab as this method of insulation would have resulted in all the problems associated with raising the floor level. Unfortunately, on investigation we discovered that the depth of the concrete slab in the middle of the room was little more than a few cm's. We were also concerned that by excavating the floor we would weaken the brick structure below. For these reasons a decision was made to drop this measure in favour of increasing insulation levels elsewhere to compensate

Our initial design proposed insulating between the floor joists with 150mm of PIR insulation board. This would have improved the U value from 0.81 Wm2K to 0.18 W/m2k. However, as the floor joists were 200mm deep we decided to utilise the full depth of the joist and increase the insulation depth to 200mm (2x100mm Celotex boards friction fitted between joists to minimise air leakage). This results in a U value of only 0.11Wm2K. When insulating in this way it’s important to insulate between the last joist and the outside wall. Also, you must maintain cross ventilation in the cellar to remove moisture and prevent timber rot and mould growth. For fire protection purposes the ceiling was finished with 12mm layer of masterboard

Air leakage due to gaps between the skirting and the old floor boards was identified as a major air leakage pathway during the air tightness testing. To resolve this the air tightness strategy adopted for the project included replacing all the old boards above the basement (front lounge and hallway) with 18mm chipboard – as can be seen above. Notice that any gaps between the new skirting and floor have been sealed with polyurethane foam.

There is heat loss from the living space on either side of the cellar stairs (from the back lounge and hallway).

To address the heat loss from the internal rear longe wall into the basement we have applied insulation board (Kingspan K17) to the stairwell wall. Insulation has also been fitted to the underside of the stairs to address heat loss here.

All the external walls have had a parge coat applied prior to drylining. Adding a parge coat helps improve the thermal performance by minimising air leakage through cracks and unfilled joints. For this we used a product called Gyproc Soundcoat Plus by British Gypsum.

The parge coat has been applied to the front external wall. Notoice that the partion wall between the hall and front wall has been partially removed so there is no break in the dry lining (thereby eliminating the thermal bridge at this junction).

For the side passage wall the insulation board (92.5mm Kingspan K17) is plater dot and dab bonded to the parged coat wall.

Kingspan K17 boarding lifted into place.....

It is important to keep the insulation as continuous as possible to minimise thermal bridging. We have therefore applied the dry lining between the ground floor ceiling and first floor. Gaps between the floor joists and wall were filled by applying a parge coat.

Side kitchen window has been successfully fitted. Notice the aluminium extension sills. These have been specified with a projection of 130mm to accommodate the external insulation and render.

The windows and external doors specified for the project are supplied and fitted by the Green Building Store using their Ecocontract window range. Ecocontract timber windows are triple glazed, argon filled and feature 'soft coat' low emissivity coatings combined with warm edge space technology. This results in a whole window U value of 0.9 W/m2K.

The front room bay window was installed in three sections. All window reveals are to be insulated with 60mm Kingspan K17 insulation boarding, walls to be parge coated and dry lined. The Ecocontract timber windows and doors are all accredited under the Secured by Design scheme and have Forestry Stewardship Council (FSC) certification.

Both the front and back external door have been replaced with bespoke timber doors supplied by Green Building Store using their Ecocontract range. The doors have a U value of 1.4 W/m2K. The front door reveals in the picture above will be insulated with Kingspan K17 insulation board. Walls to be parge coated and dry lined.

Defective bricks in front and back chimney have been replaced and repointed. Front chimney is no longer required and has therefore been capped.

Like many terraced properties the property has an alley way that is responsible for significant heat loss from the bedrooms located directly above. To address this 150mm PIR insulation boarding has been fitted to the ceiling of the alley. This will also help reduce air infiltration that was identified during the air pressure test carried out during the design phase of the project.

For secondary heating we will be installing a modern wood burning stove in the back lounge. To allow this the chimney has been opened up and a hearth built.

The property has had loft conversion carried out sometime in the 1980s with the addition of two bedrooms and second bathroom. To expose the existing roof structure the plaster board has been removed.

The roof above the top floor landing has been exposed to enable the insulation works to commence. The existing rooflight is not correctly fitted and cannot be opened. This will therefore be replaced with a new velux rooflight with a much better U value of 1.4 W/m2K.

Front bay has now been completely rebuilt. New air bricks to provide adequate ventilation to the cellar.

New steel lintol installed above front bay.

Concrete support installed to carry chimney breast above. Remaining chimney to be infilled with vermiculite

Existing air bricks in chimney breast in front and back bedrooms bricked up.