I can give you the opinion on clearance reduction as most US codes and testing agencies see it. http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_24_sec007.htm The short story is that a 1" air gap is required behind the heat shield, and something more substantial than foil. TABLE G2409.2 (308.2) REDUCTION OF CLEARANCES WITH SPECIFIED FORMS OF PROTECTION Should give you a good idea of what "should" be an acceptable means of reducing clearance. Think of it as a double boiler system. If you put a pan directly on the heat, you can burn things very easily. But, if you put one pan inside another with boiling water, then it keeps things from getting too hot.

I find Weather Shield easier to use and if applied correctly, very good. Sandtex is I think tougher but clogs brushes and rollers if you are not experienced with it.

what is the level of insulation provided by glazings and new walls? especially glazing, to avoid dispersions... ideally radiators should be close to the cold points (glazing, again) to balance the environment and shield the incoming cold. The corner with the table seems the best option, if I translate this plan into a finished space. Other factors: Curtains can help. Solar gain (exposure) can help. A dark paving outside can help (absorbs sunlight and releases heats slowly). I often say it's better to consult an architect in advance, dear, because of matters like this that get pointed out during the design... But do not desperate, just make sure the insulation is good and the glazings are good too!

Hi, Karen again. Have just drawn out a sketch from yours. My first thought is, having lived in Yorkshire for a 18 months and experienced the wind, why not hedge completely? This might sound expensive but if you buy bare root through a local nursery it is very affordable. Now is a good time to plant. Our garden is affected by high winds as we are in an exposed spot. We are fortunate to have inherited a very mature holly and cherry laurel hedge which is a fantastic wind break. Wouldn’t recommend laurel as it is very fast growing and so makes for a lot of work. The hedges we have planted are mainly yew. These grow surprisingly quickly, in the right conditions(they hate being waterlogged and it will kill them). The yew is used within the garden to compartmentalise areas and restrict views as the garden is on a slope and would otherwise be fully visible at first glance. However, on the boundaries we planted a copper beech hedge (stunning in full leaf) and a native hedge. The native hedge has been laid and is so beautiful. We had it done by a chap who works in National Trust properties. I have done some hedge laying,having chatted to him and, while I cannot produce the quality that he can, it is possible for it to be done by an amateur. I’m sure you could find videos on line. Laying strengthens and thickens a hedge making it a better windbreak. I wonder of your existing hedges could be laid. Unfortunately I have to stop now as I am planting tulips. A dear friend, now sadly dead, used to say “you can’t have too many spring bulbs” and she was right. ridiculously cheap. Native hedging is wonderful