Sealing
Overview | Doors and Window Frames | Skirting Boards
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Sealing your house solves problems and introduces new ones. On the one hand sealing stops cold air coming in and hot escaping in winter. On the other hand a totally sealed house has no airflow in it, and becomes uncomfortable and stale (there is a study on the rate of airflow around a room that is seen as comfortable - it also covers humid/dry and hot/cold living, and where the human comfort zone is – pg 66 The Natural House Book as well as pg 77 of The Good House Book. The same book covers designing houses for local conditions – hot/humid/arid/temperate/cool pg 69 The Natural House Book).
Local conditions will really dictate the best design – in very cold places, totally sealing and then having a mechanical device (using minimal electricity...) might be best (see Passive House as a leading edge example of this – as well as a great site on energy efficient construction).
In general having well fitting windows and doors, with minimal gaps, will help in keeping warm air in the house in winter – even keyholes can let blasts of cold air in. In South Africa where we legally need air bricks in most rooms, sealing totally is not possible anyway. If you were to seal totally, you would want to install a heat exchange – probably a mechanical one that can push stale air out of the house, bring fresh air in, but exchange the heat in the process – so that the fresh air gets the heat (or coolness) of the stale air. Do a search for Residential Heat Recovery Ventilator to find overseas models.
The only product we've come across in South Africa is strips of foam with a peel-of sticky back. Overseas there are variations of this using rubber designs that are far more effective, come in different shapes and sizes etc.
The best solution is to have windows and doors that fit to start with. Aluminium and PVC windows and doors offer the best solution here, especially higher quality ones that come with rubber seals in all the frames. Unfortunately aluminium and PVC have large footprints in their production, and are not environmentally friendly.
That leaves wood. In South Africa the demand for wooden door and window frames is so high that most wood is not left to dry properly, so that after a while gaps do appear due to warping. Very good quality frames with good fixtures for the windows are a good compromise. It's better to oil wood than paint or varnish – with paint or varnish you're adding layers to the outside of the wood (apart from the initial primer), and thus changing the size of the frame and door/window, and thus affecting the fitting of it. There are some links under Glazing for suppliers.
For larger gaps in joints professional carpentry/masonry work will of course be required.
If skirting boards don't fit flush with the floor, you will have an air gap where air can escape. Either refit them or fit a secondary rail along the gap. Consider before filling the gap with a foam filler – these have an awful environmental footprint in their production and can release harmful fumes (pg 214 Living Spaces).