Hare Cottage and Barn
Solid Wall Insulation, Air Source Heat Pump, Mixed Insulation Systems, Natural Materials, Recycled Materials, LED lighting, Primary and Secondary Double glazing, Heat Recovery Ventilation, Solar Thermal Water Heating, Home Automation.
Hare Cottage is a thatched mediaeval “Hall House” that is believed to date back to around 1550. The Barn, is situated to the rear, and may be more recent, but has had a long history of alterations that have come to light during the process of upgrading.
The cottage is a listed building with many period features and limited scope for dramatic thermal improvement, without compromising the historical integrity of the building.
The Barn Project:
The aim of this project was to upgrade the barn to provide a spacious multi-use family living space with home office facilities whilst retaining the large garage and workshop space. The building had an office/studio on the first floor, and the rest was storage. There was a degree of insulation in the office area, but it was difficult to use in the summer, as it was too hot, or the winter, too cold! The building is also listed but the planners allowed us a greater degree of flexibility due to the fact that the building was “curtilage listed” and was not considered to be of significant architectural interest.
We wanted to achieve a high level of insulation, to minimise running costs, but had several factors to deal with. There are no foundations or damp proof course and there was evidence of rising damp, though this was probably caused by a combination of a concrete floor and gypsum plaster on the walls of the ground floor workshop. So, for the lower part of the building some form of breathable insulation that would allow the damp to “escape” would be needed. The roof construction was substantially altered to provide head height upstairs, but it was felt that adding substantial weight or thickness was undesirable. The third substantial area to be insulated was the garage ceiling, and this needed to be airtight and fire resistant.
We settled on four different insulation technologies.
For the garage ceiling, Warmcell recycled paper insulation, blown in from above will provide a high level of insulation, and air tightness. The vaulted roof has 155mm of Celotex which gives a high degree of insulation without losing too much ceiling height. Celotex is light weight and relatively quick to install. The roof is ventilated above the Celotex using the “cold roof” method.
The external walls of the occupied space are insulated with Tradical Hemcrete, from Lime Technology a company based in Abingdon. Hemcrete is an unusual material that can be used for complete wall construction in new build properties, or as an internal or external insulation. The density can be varied when mixing the components altering the balance between thermal mass and insulation. We used two different densities depending on location. The standard density sections are about 200mm thick and give a u-value of about 0.35.
In other areas we have used 150mm of lower density hemcrete behind Resistant Multipro breathable boards, giving a similar u-value. Hemcrete has higher thermal mass than many insulation systems, resulting in slow warming and slow cooling, that suits the cyclical use of domestic buildings and can, according to some studies, give much better overall thermal performance than the basic “u-value” would suggest.
The material is made from the stems of hemp plants and a lime based binder and was mixed in a cement mixer and cast in situ using temporary framework and shuttering. Its a slow process for two people and one small mixer. Ultimately the material is recyclable and compostable. With a traditional lime plaster finish we have constructed walls with considerable character and texture which suits the building.
The rear wall adjoins another cottage, here we have used multifoil insulation behind a reed backing and lime plaster to give a degree of insulation without making the wall thickness too great, allowing us to leave some of the original stonework exposed.
Adding new materials to an old building rarely gives an aesthetically pleasing result. We were forced to use some steel joists and some new softwood support columns to support the roof but we have managed to source recycled and historic materials for flooring and many structural features, such as using a section of old roof timber to support the stairwell and recycled timber framing to support wall boards and the bathroom wall. This wall uses wooden panelling removed from the main house in previous years. The external and bathroom doors are reclaimed. Care was taken to source any new wood from sustainable sources.
Windows are a high priority for conservationists and getting listed building consent for even double glazing is difficult, so we opted for a system of secondary windows, leaving the original windows, of various eras, intact. In the rear of the roof was a large north facing window, almost 3m wide and 2m high, made from wired obscured glass. It provided a nice light, but an open hole for heat loss, so we constructed a new window inside, using 24mm double glazed glass, sealed to the roof timbers. The gable end window on the first floor is a 1950s metal casement, and this is supplemented by an internal opening double glazed window constructed on site from reclaimed oak from old church pews, and the small downstairs window has a secondary window aligned with the inside of the wall, to minimise heat loss here. The single “velux” rooflight has been replaced with a pair of low profile rooflights by Lumen that combine traditional metal framework with hi-tech double glazed glass that is heat reflective to minimise heat loss and heat gain. The glass is also self cleaning.
The use of natural materials as far as possible was dictated to some extent by the building, materials added to it and the conditions of the listed building consent, but these finishes also have benefits for the occupants both visually and environmentally. All wall finishes are breathable, mainly being traditional lime plaster which moderates internal moisture and may absorb and neutralise some atmospheric pollutants.
All paint finishes are clay paint which has no unpleasant vapours and does not impair the breathing wall construction. Floors are wood, oak in the high traffic office area, and recycled and original pine on the first floor finished with natural water borne pigments and traditional Danish oil. The vaulted ceiling is finished in canvas to keep weight low and to improve the acoustic performance of the space. One section is clad in reed board. The walls of the bathroom are recycled panels from the main house. The wall boards are magnesium silicate which performs like plasterboard but is breathable, hygroscopic and recyclable. It isn’t an easy substrate to plaster! Waterproof finishes in the bathroom are conventional ceramic tiles and recycled rubber.
Ventilation and Heating,:
The bathroom extraction is handled by a heat recovery unit that provides a constant inflow of fresh air and warms this air by recovering heat from the outfow air. Although the design of the building is intended to minimise the heating requirement, the household needs hot water and space heating. The original heating system for the house and water was electricity. Gas is not available locally and oil was rejected on both practical and environmental grounds. We briefly considered wood pellet systems but these were rejected on cost grounds and the fact that smaller systems tend to be based on room heaters that have a heat output to the room when heating water. This would mean that in a highly insulated space we would be unable to heat water by this method for many months of the year as the room would get too hot! We finally decided on a system based around an air source heat pump, as we don’t have the space for ground source. Had we made this decision earlier we may have opted for under floor heating in the ground floor office, but underfloor heating on the first floor wasn’t advisable due to the old wooden floor we wanted to preserve. The ASHP lives outside, it is large, grey, and has a big fan on it. At first it seemed noisy but we realised it was actually next doors oil boiler flue making the noise, so its not silent, but its far from noisy. The unit heats water, and runs three heating zones. As the barn will be occupied on an irregular schedule the heating is on manual control, though triggered using computer controlled radio switching. This means we can switch the heating on and off from anywhere via the internet. During the summer the water heating will be provided by two solar panels on our south facing roof. These were not commissioned until October, but still provide remarkable amounts of hot water on bright days. The water and heating systems also connect to the main house via 13m of buried highly insulated pipework, providing background heating in the cottage and all our hot water.
The uses of the building dictate a flexible approach to lighting design. We have two lighting circuits in the office area, using downlighters equipped with the latest LED bulbs. We have a mixture of warm and cold white lights to enable colour photographs to be assessed in a range of lighting temperatures. Each light is 5w allowing the room to be light to a very bright level with a total consumption of 40w. Upstairs there is a combination of LED spotlighting using the latest 3.6W GU10 LED bulbs and high efficiency T5 linear fluorescent lights using high frequency dimmable ballasts, so we get highly controllable even lighting. Colour changing LED strips give “mood” lighting, and low voltage LED strip lights light the bathroom. With all the lights on full, the total power consumption will be 110w.
There is a small unit in the office, connected to one of the network ports that allows us to switch various electrical devices on and off via a computer, either automatically via timed “events” or manually. This allows very precise control over the heating system and allows us to switch lights on and off via remote controls, which has in turn, simplified wiring and reduced the amounts of cabling that has been installed. It also allows us to switch off the lights remotely if accidentally left on!
At the time of writing the barn is not in use, so the practical day to day issues and performance of the building are still unknown.
We have been living in the cottage for just over five years and it has proved to be a very comfortable small family home. We have fitted a modern kitchen, using low energy consumption appliances and the lighting has been upgraded as technology has improved and we have a mixture of tungsten low voltage, CFL and LED lighting. It is likely that we will move to more LED lighting as funds allow.
Old stone and thatch buildings are rarely airtight, but subjective comfort can be modified by reducing air movements in occupied areas thus reducing heating demand, even if actual temperatures are not greatly affected. To this end we have paid attention to sealing the opening casements of the relatively old windows on the front elevation, and we will be supplementing this with secondary frameless double glazing to the four front windows. We only have one door into the house, off a lobby with two external doors. The main door into the house is efficiently sealed, and the lobby is unheated.
Modern living tends to generate moisture levels that ancient buildings were never designed to deal with. Cooking, showering and the generally higher indoor temperatures expected today all contribute to higher moisture levels. Condensation is the result and the house is showing signs of deterioration such as mould growth and rotting of window frames. We have designed and installed a whole house ventilation system with heat recovery, which removes warm, wet air from the kitchen and bathroom, and providing warmed fresh air into the three bedrooms. This has proved a great success, radically improving internal air quality.
Although solid wall insulation would seem to be a logical addition there is actually little scope for installing conventional solid wall insulation systems as the walls are neither flat nor vertical. The textured surfaces are part of the history and aesthetic appeal so hiding them would not be appropriate. We will be installing an area of phenolic insulation in the bathroom along with the secondary double glazing to reduce heat loss in this area, which was identified as a cold spot by thermal imaging.
Thatch is considered by many to be a good insulator, but the reality is that it is far from airtight and thatched roofs are generally steeply pitched leaving a large loft space, which if not converted, can take a lot of heating. We have installed about 300mm of conventional glass fibre insulation with some areas of solid insulation for storage. This leaves some “weak” areas above the windows which we may insulate when we next redecorate.
The windows to the north facing rear elevation were modern double glazed softwood windows, in poor condition. We received planning consent to replace these windows with historically correct but double glazed hardwood windows which will provide service for many years and reduce heat loss through more efficient double glazing. Having hand made oak window frames made for older buildings is not cheap!
Changing the fabric of buildings can have an impact on carbon emissions, but the root cause is how we run our lives. Although influencing behaviour is a difficult and inexact science, especially with teenagers in the household we have established a culture of shorter showers and the use of light switches to both switch on and switch off lights. Fitting PIR sensors in key areas stops lights being left on, and avoiding standby facilities by use of home automation systems has reduced our basic energy consumption by a small, but significant percentage.