Garage conversion - foundations and garage floor question

[AlVal]

I'm about to convert an integral garage from my 1993 build detached house.

there is a tarmac drive leading up to the garage door.

Although I'll be contracting the job out, I want to have a good understanding of the work required, and I have a couple of questions:

1. The "trial dig" to establish what foundation lies beneath existing garage door in order to support new bricks/window - is it normal to dig away the tarmac in front of the garage door to find the foundation, or to do it by smashing through the garage concrete floor on the inside and looking from the inside so as not to damage the tarmac?

2. Building regs, insulation etc in regards to flooring - what's the best way to tackle the flooring, is it normal to dig out the existing garage concrete floor? I'm particularly keen to make sure I understand this bit, especially in order to get the best thermal efficiency - what's the "best" way to approach it, how many layers are there to a proper floor, and what should they be made of? where do "thermal breaks" etc need to be placed?

Thanks

Alan

 

[RNReindeer]

I can't give you a definitive answer 'cos I'm only a DIYer.
But you'll probably need 100mm insulation, either below the screed or below the concrete.
There are other factors to be considered, Under floor heating and type of floor in the finished garage, and existing difference in height between garage floor and house floor.

Let's assume, for simplicity, that there's no UFH and it's a solid floor proposal.
You'll have appox 150mm well compacted hardcore, 50mm sand blinding, DPM, 100mm insulation, 100mm concrete, approx 50mm screed.
That's up to 450mm, some of which might already be there, but there's only one way to find out.

So given the option of breaking up the tarmac, or breaking up the garage floor, which will probably have to be broken up anyway, my guess is that the exploration of exisitng structure may as well be done in the garage, out of any inclement weather.

I assume you won't want tarmac up to the finished conversion walls on the outside, so some tarmac will need removing, but not essential.

Thermal breaks are around the perimeter between walls and concrete floor.

 

[AlVal]

Thanks a lot for taking the time to post that informative answer,

I had assumed solid floor, yes (unless any other non-solid method is in some way superior?)

what kind of insulation material is used (or rather what's the best kind to use?) below the concrete floor, and is the same insulation material used to make a thermal break around the edges?

 

[RNReindeer]

This will give you an idea of the underfloor insulation and prices:
http://www.insulationwarehouse.co.uk/kingspan-insulation.htm

Assume 100mm for costings. Buidling Regs or specs might say a little more or a little less. It may depend on the overall spec of the building, so more can be added in some elements to make up for shortfalls in others. Although the age of you house shouldn't present problems.

The perimeter insulation is of a similar material but can be substantially thinner, perhaps 25mm. The insulation reaching from the top of the screed down to the underfloor insulation to avoid any cold bridging from wall to floor mass. Again, Building regs will specify.

I've cut pieces that slide down the sides of the underfloor insulation because they are then easily held in place.

 

[freddiemercurystwin]

Frankly I can't be arsed to read the other replies (I don't have the time today) but generally the existing slab will be beneath your existing finished floor level, so generally you add a dpm, some celotex (depending on the level difference) and then a minimum 60mm screed, you always do your trial hole in the tarmac digging up the the concrete is nuts. So begs the question what is the height difference?