‘Passivhaus’ extension completed

‘Passivhaus’ extension completed

The extension to this 1960’s bungalow is now complete and the big question is how it will perform in hot weather.  It was always going to be difficult to prevent overheating due to the walls of glass to the south and west!  I would argue that overheating should be designed out completely to maximise the use of a room and allow some flexibility as the climate changes.  Often a more practical approach is requested and as the room is not a bedroom and is only for occasional use, a higher level of overheating can be acceptable.  The usual strategy was employed; model in PHPP, include high levels of insulation to limit heat gain through the fabric and use cellulose insulation to add (some) thermal mass.  But it’s always the fenestration which is the most critical and this was very carefully considered.  There is only one rooflight and it faces east with a basic internal blind.  The window also faces east and benefits from the very effective Internorm HV350 integrated blind system so should contribute negligibly to the solar gain.  It’s the south picture window and the west slider which are the real issue and the only effective solution here is to fit external shading.  The architecture didn’t allow an overhang or brise soleil, so a vertical shading device was the only option.  Unfortunately, the external venetian blinds were omitted due to cost and their effect on the eaves and only internal blinds were fitted.  While these internal blinds work well for privacy and control glare, they are be dramatically less effective (perhaps 30%) as compared to external blinds (maybe 80 – 90%) which is what would be required for adequate solar control.  However, the owner has a well resolved strategy for the blinds and as the site is elevated and near the coast there is often a good breeze and the multiple options for opening fenestration to dump heat (including secure ventilation options on the slider, rooflight and window) mean the overheating can be mitigated to a large extent.  It’s always a balance and it will be interesting to see if the extension remains habitable during prolonged hot weather, but then perhaps it doesn’t matter as the room is not a necessity just a lovely place to be.

‘Passivhaus’ extension

The extension to this 1960’s bungalow is now complete and the big question is how it will perform in hot weather. It was always going to be difficult to prevent overheating due to the walls of glass to the south and west! I would argue that overheating should be designed out completely to maximise the use of a room and allow some flexibility as the climate changes. Often a more practical approach is requested and as the room is not a bedroom and is only for occasional use, a higher level of overheating can be acceptable. The usual strategy was employed; model in PHPP, include high levels of insulation to limit heat gain through the fabric and use cellulose insulation to add (some) thermal mass. But it’s always the fenestration which is the most critical and this was very carefully considered. There is only one rooflight and it faces east with a basic internal blind. The window also faces east and benefits from the very effective Internorm HV350 integrated blind system so should contribute negligibly to the solar gain. It’s the south picture window and the west slider which are the real issue and the only effective solution here is to fit external shading. The architecture didn’t allow an overhang or brise soleil, so a vertical shading device was the only option. Unfortunately, the external venetian blinds were omitted due to cost and their effect on the eaves and only internal blinds were fitted. While these internal blinds work well for privacy and control glare, they are be dramatically less effective (perhaps 30%) as compared to external blinds (maybe 80 – 90%) which is what would be required for adequate solar control. However, the owner has a well resolved strategy for the blinds and as the site is elevated and near the coast there is often a good breeze and the multiple options for opening fenestration to dump heat (including secure ventilation options on the slider, rooflight and window) mean the overheating can be mitigated to a large extent. It’s always a balance and it will be interesting to see if the extension remains habitable during prolonged hot weather, but then perhaps it doesn’t matter as the room is not a necessity just a lovely place to be.

‘Passivhaus’ extension

Low energy renovation of a bungalow in Rottingdean including loft conversion and side extension. The existing roof was transformed by stripping back to the frame to utilise all internal space, adding deep rafters alongside the existing to super insulate with 300mm of Warmcell (cellulose insulation). High performance airtightness, windtightness and triple glazed rooflights complete the building envelope.  More details and images