Ventilation is a big issue these days. We need good clean air to live. As you may have noted from elsewhere in this project blog, the need to manage humidity and condensation in a timber framed building is of great significance. This, above most other things, has been a guiding principle impacting most design decisions on the refurbishment project. The installation of an efficient mechanical ventilation and heat recovery (MVHR) system was anticipated at day one and carefully integrating such a system into the cottage was always going to require forethought and care.
The system is simple. Fresh air is drawn in from outside and passed to the internal living rooms of the cottage, but only after it is pre-heated by exchanging heat from warm moist air drawn from the bathrooms, WCs and kitchen spaces. The extracted waste air is then exhausted to the atmosphere. The system is said to be over 90% efficient.
Our system was supplied as a ready to install kit. However, given the constraints imposed by the building’s listed structure, we needed to find ways of installing the MVHR unit, plenums and the ducting without compromising the historic fabric. The MVHR unit is sited in the small loft space above the bathrooms. This makes for easy access to the eves for the supply and extract air ducts. The MVHR unit air filters can also be accessed ready for regular cleaning and maintenance.
The supply and extract ducts radiate from a pair of stainless steel manifolds, the number of supply and extract ducts matching as far as possible to enable a “balanced” system. Whist this would be especially important in the case of a fully sealed “passive house”, it is good practice in this case notwithstanding the inevitably “leaky” nature of this historic building refurbishment. The real benefit will be minimising the potential for humidity and condensation build-up without the sacrifice of heat loss, particularly during the winter months.
The challenge of threading up to 15m of ducting to the various extremities of the cottage was overcome by making use of one of the four chimney flues that extend through the full height of the building. Three ducts were dropped down the flue through a small aperture in the loft side of the stack. The flue used to serve the lower ground floor fireplace at the bottom of the building, so it provides a ready and direct route for supply air to the most distant parts of the building.
One day soon we’ll be switching the system on for the first time, so hopefully it works as I intended!
The metal structure with its cantilever roof has now been measured by the glass fabricators in anticipation of the glazing being installed. This was to have been in around twelve weeks time. Not now I’m afraid. Like everyone else, we’ve been struck by the global Covid-19 virus pandemic and this has hit our supply chain.
Prior to the pandemic hitting we did manage to get the porch’s timber structure and insulated warm-deck roof formed, ready for cladding and finishing when conditions allow. The roof-light aperture and the extent of glazing is now apparent and the roof structure appears to magically float, completely unsupported adjacent to the cottage – it’s going to look fabulous!
Work is still progressing slowly on the interior. Steve and Healey are continuing to work for the sake of their own livelihoods, at least until such time as authority dictates otherwise. Strict social distancing measures, however, require that I cannot be on site, which is an enormous frustration. In the circumstances I’m going to use this time of enforced isolation from the cottage to try and bring this blog up to date and provide further details of what was happening prior to the pandemic hitting.
The team from Argles Medal Design have now installed the steel structure to form the porch extension. The huge cantilever is amazing, structures always fascinate me and this is no exception! The clear unsupported open corner that will be possible when the glazing is opened up will really make this space. The social spaces within the ground floor to the cottage will hopefully spill seamlessly into the courtyard/garden outside. It should be a fabulous space for its small size.
The entrance to the cottage will be through a starkly contrasting contemporary glass and steel “porch”. The foundations for the structure were put in place a year ago before the scaffolding was erected, but now the scaffolding is gone, we can get the extension fabricated.
This is the most expensive single element of the project involving use of “weathering” or COR-TEN® steel: https://twopointseven.co.uk/blog/f/what-is-cortenweathering-steel . Weathering steel, best-known under the trademark COR-TEN® steel, is a group of steel alloys which were developed to remove the need for painting and form a stable rust-like appearance when exposed to the weather for several years. Consistent with my aim for a truly sustainable restoration of the cottage, weathering steel is not only made from recycled steel, it is also 100% recyclable itself.
Almost a year to the day, the scaffolding around the cottage has been gradually removed to reveal the refurbished exterior with its beautiful natural slate roof, repaired chimney stack and the crisp white larch cladding. The rainwater down-pipes still need to be completed, but these must wait for the drains to be connected. The windows also need installing and these are going to wait until the interior work is complete as they can be fitted from within. Everyone involved is chuffed to bits!
The confined nature of the site at 28 Leigh Hill has meant we’ve had to find space to store salvaged wood, materials awaiting use, and a place to do preparatory painting. A pair of vacant shops nearby have proved invaluable for this purpose and without them, we’d have been falling over ourselves at Leigh Hill. Once the the interior wood wool insulation arrived, we virtually filled a shop with the insulation batts.