Air Tightness

Draughts are horrid and cold. Not only that though, energy wastage due to air leakage might account for 20% of heating demand (a higher proportion in new properties that are better insulated), perhaps £120 a year in our case, so careful attention to air tightness is an essential part of any low energy building.

The objective is to stop as much uncontrolled air flow as possible, by sealing up all the gaps, holes and cracks in the building fabric.

Ventilation, however, is essential for a healthy building. This is the controlled flow of air, and the objective is to replace stale, smelly and damp air.

Achieving good air tightness requires an attention to detail that most builders would consider anally retentive. But that’s because most builders are too rushed to do a proper job, so a third of new houses don’t even meet building regs.1

 

As well as around windows and doors, air leaks in through lots of places you might not expect. Our kitchen cupboards are particularly draughty, I notice. Photo: Energy Saving Trust
As well as around windows and doors, air leaks in through lots of places you might not expect. Our kitchen cupboards are particularly draughty, I notice. Image: Energy Saving Trust guide
New houses are tested for air tightness by installing a massive fan in the door, 'inflating' the house, and measuring how quickly the air leaks out. Photo: Energy Saving Trust
New houses are tested for air tightness by installing a massive fan in the door, ‘inflating’ the house, and measuring how quickly the air leaks out. Photo: Energy Saving Trust guide.

Measures I took to improve air tightness included:

  • Self adhesive rubber weather strip fitted to the edge of a wooden window that no longer sealed tightly
  • Rigid draught proofing strips fitted to the loft hatches – done by the installers when increasing the loft insulation
  • Key hole covers fitted and an unused cat flap boarded up, before new doors were fitted
  • Plastic sheeting under the floor of rooms downstairs, taped around the edges to insulation boards or walls  (see Floor)
  • holes & gaps between floorboards in the hall filled  (see Floor)
  • after refixing skirting boards, sealed along the edges with decorator’s filler (which also disguises imperfect cuts!)
  • edges of window frames and bays taped to the walls before fixing insulation boards (see IWI)
  • when the upstairs internal insulation was plastered, the plasterers were asked to apply the lime plaster around the ends of the floor joists
  • sealed around pipes where they penetrate external walls, eg; pipes for the new heating system in the garage

 

Light fitting wires penetrating ceilings can cause air leakage to the roof space above.
Light fitting wires penetrating ceilings can cause air leakage to the roof space above.
 I sealed these rough holes with decorator's filler or sealant. I did most from the loft above.
I sealed these rough holes with decorator’s filler or sealant. I did most from the loft above.

 

1. … in a recent study of 100 new dwellings … none achieved the best practice performance of 3m3/h/m2. The research, undertaken by the Energy Efficiency Partnership for Homes, showed that around a third even failed to achieve the worst acceptable permeability (10m3/h/m2) expected in the new building regulations Energy Saving Trust