Make sure you specify air tightness and have a blower door test done as part of the construction process. If you're building airtight, you'll also need a properly designed Mechanical Heat Recovery Ventilation System. You'll get the best return on investment for this detailing, followed by insulation. Windows, despite what many people think, once you get to double pane are low on the list of areas that make much difference to your overall energy usage. If you're going GSHP see if you can specify a desuperheater to provide some hot water too - though if you're going fully water-to-water (i.e. radiant flooring) you'll probably have this ability anyway. Might be worth considering investigating solar thermal too - though in the highlands of Scotland this will be of limited benefit (at least, the holidays I had there as a child seemed rather less than sunny than I'd have liked).

Hope this helps,

Paul in Montreal

Seems timber cladding is not considered 'appropriate' by the powers that be due to the lack of tree plantations in the locality. Also, we are subjected to severe winds and driving rain which makes blockwork 'feel about right.'
Interesting ideas so far though, guess I need to read up on air tight construction and heat recovery systems !

Using concrete blocks doesn't always have to be as bad as it may first seem so don't beat yourself up about it if you feel you have no alternative.

I used blocks that were manufactured less than 2 miles away so final transport impact was minimal. Cement can be made with a large energy input from burning old car tyres that otherwise would go to landfill. Thermalite claim that around 40% of their content is recycled material.

By the time you come to sell the house, Tom, energy will be so dear buyers will relish the idea of a house which doesn't need, or have, a central heating system and will be falling over themselves to pay you your asking price rather than saddle themselves with crippling utility bills. I like the idea of wood or multi fuel stove for back up heating and hot water in the winter months. If you used one of those log maker gadgets to turn all your waste paper and card throughout the year into "logs" you might never need to by any fuel again. Plus there are always opportunities for scavenging scrap timber. Why pay out for something you don't need?

Tony, I thought you were for externally insulated solid walls rather than cavity? I can't believe that a wall with 2 skins of 100mm blockwork and a 300mm cavity is structurally as good as a 215mm solid wall with external insulation, so perhaps a solid wall could be narrower than this and still be as good structurally as the cavity wall? If you could build a house out of a single skin of 140mm blocks with external insulation, there has to be a cost saving over the cavity wall construction. Do you think this would be allowed?

My highland project was a disaster and never got off the ground. Which LA are you under? Lochaber are a nightmare,

It is not difficult to lay with mortar. There is a surprising variation in sizes if blocks to go dry also I much prefer solid or poured concrete.

Building control should be there to help you get it right but they love to pass the buck ( their responsibility ) to others.