Concerns identified are condensation; inadequate levels of loft and wall insulation, particularly in the rear annex; the structural integrity of the rear annex; and the thermal response time of the main part of the building.

Whilst considering all of the possible remedial improvements as a whole, the ease and benefits of making improvements to the annex might be outweighed by those of rebuilding it. 

Monday, 21^st August, 2006

The property was inspected in response to a request from the client to recommend  further developments and repairs to maximise thermal performance whilst minimising environmental impact. The visit gave us a good understanding of the building’s construction and the function of the construction elements. This report will explain the issues identified during the site visit and set out our recommendations.

The client's original brief asked for information on thermal performance, solar hot water and natural materials. The remit of this report has been expanded to address the repercussions of developing the following: downstairs bathroom, kitchen, en-suite bathroom window, old carpets, fireplaces and chimney breasts, unwanted artex, and old wallpaper.

The main areas for concern that we have identified are:
- Condensation
- Inadequate levels of loft and wall insulation, particularly in the rear annex
- Structural integrity of the rear annex
- The response time of the building.

This report sets out specific recommendations in order of priority. The client was encouraged, whilst considering all of the possible remedial improvements as a whole, to bear in mind whether the ease and benefit of making improvements to the annex might be outweighed by those of rebuilding it. We have referred to the possible benefits of this option in our recommendations. 

General overview and construction

The property is a south-facing two-up, two-down semi-detached cottage situated in a small village in the open agricultural landscape of Suffolk. The cottage and its neighbouring building may have originally provided accommodation for the windmill, which once stood directly in front of the property. A rear annex was added later,  and is possibly Victorian. More recently, a single storey extension has been built, which connects the annex to the neighbours’ annex.

The oldest part of the house is of heavyweight construction, probably brick and lime mortar, and appears to have been later rendered with cement. The roof is tiled with slates and its floor has had a layer of concrete laid, but it is uncertain as to what was there originally. A tightly winding stairwell beside the parlour fireplace provides access to the upstairs, which has two rooms side by side with a connecting corridor at the rear. Both bedrooms would have once had fireplaces. The small ‘snug’ lounge beneath has had part of the chimney removed, which needs improvement aesthetically. Although access to the loft space is difficult since both the hatch and the space itself are very small, it has been previously insulated with mineral wool which has later been added to. The eaves of the roof, which comprise a large area of ceiling above the bedrooms, are inaccessible, and appear to be uninsulated.  The upstairs corridor provides access to the annex where another bedroom leads through to an en-suite bathroom.
 
How the annex is constructed is less clear. It appears to be timber-framed with a heavyweight infill downstairs, although lightweight upstairs. Early photographs suggest that there was once a chimney at the rear of the annex, but this has been removed. It is possible that the oak frame may have been reclaimed, perhaps from an old barn, since it looks older than the annex itself. The timber has suffered extensively at some point from a woodworm infestation. Although this appears to be largely dormant, there are some signs of current activity, and the central floor bearer has been supported by a post. The timber frame’s structural integrity has been further compromised with the addition of a window, which cuts through the bracing of the frame. The walls, particularly upstairs, have poor thermal resistance. They are of hollow construction with lath and plaster. Cement render on the annex is preventing the walls from breathing, causing interstitial condensation and increasing the moisture content of the wood, which would explain the damp and consequent woodworm. The annex roof is tiled with clay roof tiles and felted with bitumen felt. The roof structure is not tied into the older part of the building. The roof space is inaccessible, but as this part of the house is particularly cold, it is assumed that loft insulation is negligible or, more likely, absent.

The single storey infill extension, which houses the bathroom downstairs, is very cold, but should not be since it is flanked on three sides by other rooms. It has a mysterious ‘missing space’ in the roof void of approximately 500 mm, which must be uninsulated. All of the property’s windows, although relatively modern, are single glazed without draught-proofing, and have no provision for trickle ventilation.

Performance principles

Solar Orientation & Solar Gain

The front of the cottage is south-facing, benefiting from 'solar gain’ (capture of the sun’s heat) for most of the day. Conversely, the north-facing back of the house loses heat through the walls and windows, since these rarely feel the sun, especially in the winter when the sun is low. To make the most of a building’s orientation, a larger proportion of glazing should face south, with increased thermal resistance to the north. Conservatories and porches can help by acting as airlocks and creating a buffer, improving thermal resistance. In this case, the conservatory is in the northwest corner of the house, although its only solar gain is received in the height of summer when the sun is high enough to come behind the house. At this time, the sun is too hot, overheating the conservatory. In the winter, when the sun’s heat is desirable, the conservatory is shielded by the house and is losing heat, particularly through radiation to the sky at night.  Conservatories can be used to good effect as solar collectors on the south side of a building, where they get the most winter sun, by acting as a greenhouse from which trapped heat can be drawn in, as long as they are closed off at night to prevent heat from the house escaping. Conservatories should not be heated. An interest has been expressed in an additional window in the en suite bathroom, on the north facing side of the building.

Our recommendation to the client:
- Only install a small window, if at all, in the en-suite bathroom since it is north-facing; or ensure that it is of a very high specification. The window should preferably face the bathroom door so light can reach deeper into the house when the door is open. Care should be taken to not cut through the building’s timber frame.
- Replace the conservatory’s glazed roof with a solid roof. This would reduce overheating in the summer, and night sky radiation losses in the winter. A solid roof would require structural alterations and possibly planning permission. A small roof light with splayed window reveals in the roof would help with ventilation, also maintaining light to the room. Improving the thermal performance of the current conservatory could enable it to be used more usefully, perhaps as a ‘transition space’ for organising car journeys.
- Consider secondary glazing the remaining panels of the conservatory and insulating the walls.

Annex remodelling potential:
- The conservatory could be considered as part of an annex redevelopment, with all of the above recommendations designed in.
- The en-suite bathroom could be moved deeper into the building with a roof light providing good task lighting. The annex bedroom could then enjoy the view to the rear from french windows complemented with a balcony.

Daylighting

The older part of the house, although the windows are small, is fairly shallow-plan and therefore daylight penetrates quite well, reducing bulb dependency. Artex and textured surfaces such as woodchip wallpaper increase bulb dependency by preventing light from travelling very far. Splaying window reveals, even slightly, improves daylight penetration, but is difficult in thick walls unless new windows are being fitted. The window on the stairwell doesn’t admit much light as it is positioned in a gully.

The annex has made the building deeper-plan, so light does not penetrate far into the rooms.  The low ceilings exacerbate the problem. Although the kitchen has large windows, the daylight is all in one corner and is not evenly distributed, and the room sometimes overheats when the sun is high.

Our recommendations to the client:
- Remove artex and woodchip wallpaper. Artex can be removed with a wallpaper stripper.
- Paint walls with white or light colours, always use breathable natural paint or a lime wash.
- Replace the stair window with a modern roof light positioned above the stairs to bring more light down through the middle of the house and improve ventilation.
- Install a seasonal sun shade, such as a pergola planted with sweat peas,  above the kitchen window to prevent the sun entering when at its highest.

Annex remodelling potential:
- Ceiling heights could be increased.
- A central stairwell with a roof light could bring light down to the centre of the building.
- High (cloister) windows could bring light deeper into the rooms from the bathroom or conservatory sides.
- Windows could be better positioned to achieve more uniform daylighting.

Breathability & Ventilation

Moisture in the walls is drawn to the driest side. Usually this is the outside, but with a cement render on the walls it is unable to escape; if this surface is cold, moisture will condense. Its only alternative is to leave the walls to the inside. This building is not suffering too badly from damp, probably because it is draughty. However, if the building is made more airtight to improve its thermal performance, damp could become more of a problem. The cement render could be removed, but this is difficult. Improving ventilation would be easier.

During the summer, a building can be cross-ventilated by opening windows, allowing rapid air exchange through the building. However, during the winter, high levels of air exchange are undesirable because of the subsequent heat loss.  To maximise the amount of moisture removed whilst minimising air exchange, it is important to recognise that the warmest air holds the most moisture. As air is warmed and rises, it is able to carry more moisture. Letting the warmest air out at the top of a building in a controlled way draws  fresh air in at the bottom. This provides slower, more efficient air exchange than cross-ventilating, and can be shut off when it is too cold.

At present, cool air is entering uncontrolled underneath doors and around windows. Unwanted draughts should be replaced with controlled trickle-ventilation to remove unwanted moisture. Controlled ventilation should be possible without compromising the security of a building so that it can continue to be ventilated whilst unoccupied.

Our recommendations to the client:
- Improve controlled ventilation and optimise breathability whenever making other changes to the house: e.g. breathable insulation in the roof space, airtight windows with trickle vents, ‘hit and miss’ vents in the floor, opening roof lights (e.g. velux) at top of stairs.

Annex remodelling potential:
- A new stairwell with a roof light in the centre of the house could ventilate the whole house.
- A fully breathable fabric could provide all the required breathability for the whole house.

Draught-Proofing & Insulation

Making a building more airtight is the easiest, most cost- effective method of reducing heat loss. When air is warmed it expands, rises and escapes though gaps around doors, windows, loft hatches etc., or through hairline cracks at junctures in the building fabric. As wind passes over a building, low pressure is created on the leeward side and air is sucked out through these same gaps. As warm air escapes, cold air is drawn in to fill the void and heat is lost. A draught felt on the floor will be reduced by fitting a draught excluder around the loft hatch, preventing warm air from escaping, and another under the front door, preventing cold air from entering. All windows, doors and loft hatches should be fitted with a flexible seal, letterboxes can be fitted with brushes, and key holes fitted with cover plates. When decorating, a flexible decorator's caulk should be used to prevent air loss through hairline cracks. When draught-proofing it is important to remember that air exchange also removes moisture from the building. Controlled ventilation must be installed (see 'breathability and ventilation').

Insulation prevents heat from being conducted through the fabric of a building to the outside.
The rate of conduction depends on the thermal conductivity of materials used. Trapped air has the highest insulation value (lowest thermal conductivity) however, if a convection current is allowed, air can efficiently transfer heat over large distances. Glass has the lowest insulation value (greatest thermal conductivity), therefore single-glazed windows are a major loss of heat. Replacing the small window area with double glazing would be more beneficial and easier than insulating the larger wall area.

Insulating the walls could help the building to respond more quickly to warmth. However, moisture in the wall would need to be able to escape, and insulation could exacerbate the problem caused by the existing cement render. There are other ways to improve the thermal performance of this building before attempting to insulate the walls.

Because heat rises, adding further insulation to the roof space should be of greatest benefit; however access to the loft is restricted. The loft is well insulated above the flat ceiling in the centre, however to the sides the eaves are uninsulated. There is insufficient space in the eaves to leave the 50 mm ventilation gap required for moisture to condense in (at the ‘dew point’), between the insulation and the cold outer surface of the roof. It would be easier to insulate the ceiling from inside, particularly since 100-150 mm could be lost internally without detriment to the rooms. Internal insulation should be breathable. Assuming that the ceiling is constructed from timber laths applied with a layer of lime plaster, then it is breathable. However, investigation would be needed to clarify whether there is a non-breathing layer already, for example foil-backed plaster board or a layer of gloss paint that could move the dew point.

Although insulating the floor would give least thermal benefit, in terms of occupant comfort, great advantage could be had. The old carpets provide minimal thermal resistance, but do reduce draughts and reduce heat lose from the feet. Warmer feet allow a lower room temperature. Insulating the floor would improve thermal comfort and negate the need for a carpet, and could facilitate underfloor ventilation.

Our recommendations to the client:
- Draught-proof doors and windows etc. and use flexible decorator's caulk when decorating. (install controlled ventilation)
- Replace the single-glazed windows before considering other measures, for example, insulating the walls. High-specification timber triple-glazed windows are available at little more cost than PVC windows, with a far smaller environmental impact.  Although this is at the bottom of this priority list, considerable benefits could be had by improving the windows.
- Insulate more where its easiest, to compensate for where its more difficult: e.g. don’t insulate the walls as this is difficult and could exacerbate the damp problems.
- Check for gaps in existing loft insulation, and consolidate where necessary.
- Insulate the ceiling in the old part of the house with natural materials as follows: batten, then counter batten, and insulate with sheep's wool to 100 mm. Lath and plaster finish. Ensure breathability, e.g. check there are no old layers of gloss paint.
- Insulate the floors as follows: batten the floor on a damp-proof course, counter-batten and fill between with a foil-backed rigid foam. We can provide further construction details if required.

Annex remodelling potential:
- The walls, windows, roof, breathability, ventilation and draught-proofing could all be specified to give the best thermal performance. A high-performance north side would enable the older part of the building to be improved less intrusively.
 

Thermal mass

The property has the potential to benefit from its heavyweight construction, as this would buffer extremes in exterior temperature. However, when unoccupied for long periods of time, it can take a long time to warm up upon occupation. Insulating the walls from the inside would reduce the area of available  thermal mass and therefore help the building to warm up faster, but as discussed above, would have problems with breathability.

The chimney needs improving aesthetically where the fireplace have been removed.

Our recommendations to the client:
- Rebuild the chimney with reclaimed brick and natural lime mortar and lime render (using gloves and goggles).

Annex remodelling potential:
- If the annex were rebuilt as a lightweight (timber) construction, it would heat up faster  than the older part of the house. The heat could then be let through from the annex to warm the rest of the building. The heavier-weight parts of the building would then retain the heat longer than the timber frame, so the two complement each other well.

Services

The cottage is centrally heated, with thermostatic valves on the radiator, which is good. There is no mains gas. The oil-fired boiler is quite modern, but there is no record of it having been installed by a Corgi-registered installer, and it is possibly releasing gas into the larder area. The boiler is also preventing the larder from being used as a food storage area because of the heat. The boiler could be moved or, preferably, used less frequently.

There are other options besides fossil fuels. A wood-powered stove with a back boiler could be installed into one of the fireplaces, reducing the need for the oil boiler.  This would also improve ventilation, and it could be used in conjunction with a solar hot water system. In the long term, a solar hot water system could be installed, or a wood pellet boiler or combined heat and power system (CHP) even shared with a neighbour. Willow could be grown and coppiced on the site of the old windmill or perhaps on the neighbouring cornfield to provide fuel for the boiler. These technologies are still in their infancy though, and given the lack of continuous occupancy, the longer term options are not a priority.

Low-energy bulbs use negligible electricity compared to normal bulbs, and the energy saved is far greater than the energy used to make the high-energy bulbs they replace.

Fridges and freezers work better in cooler rooms so that they are not working so hard to make things cold.

Our recommendations to the client:
- Replace all bulbs with low-energy light bulbs immediately rather waiting for the old ones to fail. Destroy the old bulbs!
- Use A-rated appliances
- Install a wood-powered stove with back boiler
- Insulate pipes and add an additional jacket or two to the hot water tank
- Consider moving the freezer to the garage.

Annex remodelling potential:
- The facility to later install services such as solar hot water or a  ground source heat pump could be designed into a new annex.

Water

Water is not plentiful in the area. The toilets do not have low-flush mechanisms, and these should be considered. Flushing urine uses a great deal of water, but both urine and grey water could be separated and used on the garden and willow, if grown. At present, the rainwater butts are overflowing next to the house, and are too low to get a bucket under the tap.

Our recommendations to the client:
- Install low-flush mechanisms on the toilets.
- Install a water meter, since money would be saved as the house is not occupied full time.
- Consider using  harvested rainwater in the washing machine and toilets, which would help to prevent limescale build-up caused by the hard water and require less detergent.
- Drain off the water butts and raise them up to an appropriate height for using the tap, install an inline diverter from the down pipe to the butt at the height of overflow so that water overflows into the downpipe, not from the butt (we can provide a diagram if required). The downpipe should then take the water away from the house.

Annex remodelling potential:
- As with services, potential for rainwater harvesting etc. could be designed into a new annex, whether they are required now or might be in the future.


Annex remodelling - a summary
Most of the building’s problems occur in or are exacerbated by the annex, which occupies the important north side of the building. Whilst many of our recommendations for the existing annex are easily achievable individually, taken as a whole they may be harder and more expensive to carry out. Starting again with the annex would allow the problems experienced now to be designed out, as well as allowing lighting, thermal performance, breathability, ventilation, airtightness and provision for services to be designed in. As we have stated, a high-performance north side would enable the older part of the building to be improved less intrusively. A new annex could be built using natural materials, including timber, so that the building would benefit from both heavyweight and lightweight construction.

The layout could be improved, with the following features included:
- A new central stairwell with a roof light, in the centre of the house
- Increased ceiling heights
- High (cloister) windows
- An improved conservatory / buffer space to the north
- The en-suite bathroom moved deeper into the building
- A bigger annex bedroom.

If the client is interested in discussing  ideas for the annex further, we would begin by illustrating them with some brief sketches. These would allow further exploration before detailed designs or preliminary costings are considered.


Simon Lewis