Keeping your home comfortable depends on far more than insulation

Here, George Marshall shows how to let in light, add ventilation and defeat drafts

3. Natural light

To my mind there's much more to eco-building than insulation and low-energy light bulbs. Eco houses should be airy, healthy and flooded with light; they should feel bright and fresh. So we paid special attention to ventilation and light.

Skylights are ideal in the British climate. We fitted large Velux skylights over the bedroom, mezzanine and extension (a job for the professional builder) but there is still plenty of scope for a keen DIYer to fit further internal glazing and bring that natural light deeper into a house. Glass bricks, for example, also provide good sound and heat insulation. While these should not be used for load-bearing walls, they work very well as infill. Their weight soon adds up, though, so you must first ensure the floor can take the weight.

You can lay glass bricks with glass block mortar or use silicone adhesive and special fixings. Both methods require spacers that are provided with the blocks. We chose a 15mm mortar bond with the blocks laid in a grid (like tiles) rather than a staggered stretcher bond (like a wall). Special care needs to be paid to the details of the joints because they are on display - I found that a slightly concave recessed joint looks best. We were only laying a couple of rows, but if we had laid more we would have fitted reinforcing wire along the top of each row (see

I fitted the blocks all around the tops of the walls of the bathrooms and downstairs toilet. The new upstairs bathroom has a glass panel door and, above the bath, a toughened glass internal skylight to bring more light down from the mezzanine floor above. There are safety issues here, so it is raised above the mezzanine floor and sloping to discourage anyone from standing or resting anything on it.

My only regret was that I was too timid. I hadn't realised that glass blocks provide good privacy, and in retrospect I should have built the entire bathroom and toilet walls from them. Back in 1928 the modernist architect Pierre Chareau built an entire house in Paris with glass brick walls and it still looks modern 80 years later.

4. Ventilation

Eco-architects are obsessed with ventilation, and for good reason - it is the key to both comfort and energy conservation. Most houses are either so draughty that they are impossible to heat, or so well sealed that the air becomes stuffy and stale. Although you could go for an automated ventilation and heat recovery system, I would recommend a passive system with as many adjustable vents as possible to manage the airflow. As air warms, it rises through a house, so the trick of good passive ventilation is to enable the entry of the air at ground level and to manage its movement through every room in the house as it rises.

In our house fresh air enters through the sun porch or the back of the kitchen cabinet. It rises up through the rear bedrooms or from underneath the bath, up through the front bedroom, to the mezzanine and then out though the trickle vents in the skylights.

Let's start with the ground floor. Many people with porches or conservatories open the doors on sunny days to bring warm air into the house. The problem is that this can also bring in cold air along the floor. It's better to keep the door closed and fit an adjustable vent at the apex of the roof.

So, using a short piece of drainpipe, I connected the top of the sun porch to the extension with a rotary vent of the kind that is normally fitted into windows. The huge advantage of a rotary vent is that you can see at a glance from the rotation of the vanes which way the air is moving. If I see that they are moving anticlockwise I know that air is being sucked out of the house and I close the vent. The other place where air is invited to enter is the back of the kitchen cupboard. We don't have room for a larder, so the incoming air creates a cool cabinet where we can keep the chutneys, jams, cheese and butter.

1. I made a 15cm hole through the wall and lined it, then fitted a 20cm adjustable metal vent for the kitchen side and a simple plastic vent cover on the outside.

2. Once inside the house, air needs to be encouraged to rise evenly through the rooms. To get air into the upstairs bedrooms, I knocked a 20cm hole through the wall at the top of the extension. On the extension side these are covered with a standard 25cm slatted plastic vent of the kind that are usually used on external walls. The hole was finished with cement and lined with cuttings of old thick pile carpet to dampen sound. On the bedroom side I fitted sliding adjustable metal vents.

3. In the bathroom I hinged one of the panels of the bath casing to provide a laundry chute to the utility room below. This doubles as a large vent.

All these ventilation strategies have made an enormous difference to the feeling of the house. They are especially important during the summer. We tend to forget about the impact of climate change on the summer temperatures.

Bring warmth to your house with a sun porch ...

Porches are a key strategy in eco renovation. They provide an intermediate space between inside and out, a "draught lobby" and, if placed properly, a sun trap. The sun porch differs from a conventional porch in three ways:

1. The glazing is only placed on the south facing sides of the porch: the other walls are solid.

2. The wall facing the glazing is a heat store and is painted a dark colour to absorb sunlight.

3. There is a vent or a fan at the top of the porch to bring warm air into the house.

Our porch is on the north-east side of the house with doors opening directly on to the garden. The side facing south-east is glazed, and the north-west side is solid. The glass was scavenged from a pair of old patio doors - one for the roof and one for wall - and these pieces determined the porch's proportions. With the help of our builder, Bill Frizell, we built a frame from pine 4x4s to fit the glass. To avoid rot, the vertical timbers rest on small cuttings of damp-proof membrane on top of a raised block. The roof is glazed on the south side and plywood on the north, treated with a weather-resistant deck paint.

The wall opposite the porch is filled in with the lightest blown concrete blocks, although any light infill would work. It is painted dark blue inside, which works nicely as a colour and as a heat store. We decided not to insulate the wall, but did put some spare offcuts of foam under the plywood roof. In the middle of the gable at either end, we fitted two vents: the one on the garden side is opened in summer to let out excess heat, while the vent on the house side is opened on cold days to bring warm air into the house.

And does it work? Absolutely. It is a home to our cactus collection and there is a chair for sunning in.

But if I did it again, I would do it differently: my ideal design has all of the glazing on the vertical wall and little or no glazing in the roof to avoid overheating in summer.