My house is so cold despite having full central heating double glazing, cavity wall insulation and good loft insulation. I suspect the cold comes through our integral garage which has a large gap under the door how can we seal this up? Also the house is built on a hill and has a good 3foot underfloor suspension do we really need all this space for ventilation?

my house is so cold despite having full central heating double glazing, cavity wall insulation and good loft insulation. I suspect the cold comes through our integral garage which has a large gap under the door how can we seal this up? Also the house is built on a hill and has a good 3foot underfloor suspension do we really need all this space for ventilation?
The gap for he door can be fixed by purchasing a new seal for it,a deeper seal,made by quite a few manufactures,here is Raynor doors,it is twice the thickness as a normal seal,OR,you could try raising the concrete,with a mortar pad<it would need some real professional prep work and sealing to last.

The 3 foot suspension?Is this a crawlspace? If so,insulation is more than a must,Ventilation is also a must.air must flow to keep the house from longterm moisture build up,just like a roof must be vented,so must a foundation,but a foundation just needs a little venting,not the whole 3 feet all the way around(and if you are diligent,you can block it off during the winter,as long as it is able to breath at least a little)

Hope this helps,
Ken