Originally Posted by
DarrenHW
I completely agree with all the advice Simon has given you. Most importantly he's highlighted the potential issues you will encounter with cold bridging, damp, mould, etc... yes, heat recovery will help, but will be fighting a losing battle!
Your existing concrete floor will most likely be in direct contact with the soil beneath it and through capillary action will subsequently be as wet as the ground around it, yes, the roof does offer some protection, but not as much as you'd think. As you've said, being a garage floor, it's graded towards the door opening and is therefore at exterior ground level at its lowest point, meaning rain water can find its way straight in. None of these things matter if the building is being used as a garage, there will be a good amount of air movement, very little in contact with floor and as it's a garage it doesn't matter if it's a bit damp ,it has a massive door opening and you're only going to store a wet car in there anyway!
Even if the external walls have a DPC, single leaf brick walls, are wet walls. By this I mean, when it rains the brick absorb the rain and are then very happy to pass it on to any absorbent material either touching it (timber), or near it (plasterboard) due to evaporation. Treatments and membranes can be used to slow this down, but... Again, not a problem for a garage as the walls are free to breathe, but cut off half it’s circulation and it will let you know about it!
Neither of these issues are insurmountable, nor are they necessarily expensive to remedy. However, fail to address them and you will inevitably build in problems and potentially affect the structural integrity of the building. Sorry to be blunt, but in my humble opinion, that is a risk you will be taking
I'm not playing Billy Big Bollocks and trying to piss on your parade, from your post's you've clearly put a lot of thought into this, you're emotionally invested and I imagine this will be a significant financial outlay for you. I've worked in construction full time since 2010 and I'm currently working with brick faced, timber frame houses, which is essentially what you'll be creating and I feel, good, simple, low cost building practice is missing from your plans, i.e. weep vents, cavity trays, building fabrics...
I'm quite happy to help you come up with a plan for the work (as I'm sure a number of other members will be), which will not only empower you with the knowledge to get the best out of this project, but also allow you to price materials and labour and get an idea of a timescale and finished product. I’m guessing you won’t have software to generate rendering, so if you pick up some A4 graph paper (readily available on eBay) a tape measure, a ruler and a pencil, draw out the floor plan and elevations (all from ground level) to scale (draw a 1000mm line on each page to indicate scale) scan them and upload them, I and any other member who so wishes, can print off a copy, overlay our plans and upload them with a description / explanation for your approval.
Any good contractor who's quoted on the work should have made you aware of these issues. If they haven't, they either don't know any better (unlikely), or they just want to get in, get out and get paid, will most likely not deliver on their promises and cut corners wherever they can. That said, the mention of heat recovery would suggest you do have someone who has an understanding of what will happen within the building, although it will not act as a heater, in fact it will constantly reduce the temperature.
As to the audiophile credentials of the building, I too would advocate the counter boarding of plasterboard over ply (the use of OSB instead could reduce costs) but with the sandwiching of a sound absorbing building fabric, this creates a quasi CLD arrangement and is effectively used in party walls of many apartments to meet sound test regulations.
Do you feel your corners need to be square? If you could live with losing the space, the corners could relatively easily be radius-ed having potential audible and visual benefits?
I’m surprised not more has been said about electrics. Hell yes, you should replace your consumer unit (a sub £100 investment) and make provision for a dedicated radial, associated sockets and earth. I suggest you start a new thread entitled “New HiFi Radial Install?” or words to that effect, you should receive a wealth of information, save yourself a small fortune (or spend a fortune, depending on your inclination) and if you’re really lucky get the details of a local spark who’s HiFi sympathetic?