Garage Conversion

[DarrenHW]

Does the garage have a flat or pitched roof?
If pitched, then have the ceiling follow the pitch up to help increase ceiling height.

Floor, could you do a concrete slab on celotex rather than chipboard on timber stud?
If so, cast the slab with a small gap around all sides and build the walls off the slab with flexible ties to the brick wall.

Instead of 15mm acoustic plaster on timber stud, consider: 9mm ply onto the timber stud, all joints sealed and taped, then 9.5mm plaster board over the top with staggered edges (i.e. they dont line up with plasterboard edges) all edges sealed and taped.

Best of luck

Just watch cold bridging with the floor, but it should be pretty solid if joists are fastened to slab. Don't overfill voids, more like 75% of depth, same for wall fill, and consider Rockwool instead of celotex

Regular plasterboard over the plywood. The trick is to stagger joints, and seal and tape the 2 layers independently with non-setting mastic. Just screw through plasterboard into joists should be ok.

Plywood layer also makes fitting things to wall/ceiling easier.

best of luck

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?

[Marco]

Hi mate,

You have a PM

Great post, btw. Glen, you should take Darren's erudite advice on this matter, as a builder, as trust me, he knows what he's talking about!

Marco.

[glenann]

Wow Darren! Thanks for the generous info, that’s much appreciated along with your offer too. To be clear, I haven’t had a builder in at all, the only info I have is what I have read on the subject.. I do have a friend who’s in the trade and he’ll pop round to offer some advice as well.
I’m planning to build the stud away from the outer brick wall (only about 10 or 20mm) with breather membrane on the side nearest the brick. The garage door is staying in and there will be a useable 2 metres gap between the garage door and the end or the room, which will be OSB over the stud, with plasterboard on the other side, obviously. So there will be an air gap open to the garage door down the length of the side walls (about 5 metres). After thinking about a concrete pad laid over the existing one, I’ve decided to stick to joists running the width of the garage, with the same 10 or 20mm gap all around, with the stud built on top of that.
Does that sound reasonable or again am I way off the mark here? I’m no builder but myself and a very competent friend are building it all ourselves, apart from the electrician who’ll fit the new consumer unit.
Thanks again

[JohnJo]

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?

What a cracking post and offer of help.

Round of applause required!

[DarrenHW]

Wow Darren! Thanks for the generous info, that’s much appreciated along with your offer too. To be clear, I haven’t had a builder in at all, the only info I have is what I have read on the subject.. I do have a friend who’s in the trade and he’ll pop round to offer some advice as well.
I’m planning to build the stud away from the outer brick wall (only about 10 or 20mm) with breather membrane on the side nearest the brick. The garage door is staying in and there will be a useable 2 metres gap between the garage door and the end or the room, which will be OSB over the stud, with plasterboard on the other side, obviously. So there will be an air gap open to the garage door down the length of the side walls (about 5 metres). After thinking about a concrete pad laid over the existing one, I’ve decided to stick to joists running the width of the garage, with the same 10 or 20mm gap all around, with the stud built on top of that.
Does that sound reasonable or again am I way off the mark here? I’m no builder but myself and a very competent friend are building it all ourselves, apart from the electrician who’ll fit the new consumer unit.
Thanks again

I'd be looking to incorporate a 50mm gap / cavity. The reason for this, would be to allow better air movement to help the building dry out and to avoid stagnant damp air build up. I know this will reduce the internal dimension, but in my opinion it's a sacrifice worth making. Further to this, if not already present, I'd retrofit weep vents one brick above ground level in the existing brick work. This is very cheap and simple, all you need to do is drill out the existing mortar and slide the vent in with a bit of flesh mortar to point it into place. Not only will this give the internal moisture somewhere to escape, it will aid air movement through the cavity.

Can I take it that as you're installing a breather membrane (a very good idea, I'd recommend using a reflective material) you'll be fabricating the panels and installing them as a freestanding structure within the building?

For so many reasons I'm not going to go into if you’re really not interested, I’d strongly recommend you reconsider a concrete floor. If it’s cost related, based on your original 16’ x 9’ dimensions the material cost (including 100mm insulation) would be approximately £1000. If you can operate a shovel, lift a full bucket and drive a wheelbarrow you could do it yourself comfortably in a weekend, or in a day if you don’t mind getting a sweat on! Two experience workers could easily do this in a day and would charge you ~£150 each, or you could get the insulation in and get a barrowed concrete service.
I estimate a timber floor would be a little over half the material cost so appreciate the implication, but you will overcome so many potential problem (this is why <90% houses are built this way) and have a better sounding floor that will last longer than the building it been poured in.
If you’re just not interested then I’ll leave it there and stop banging on about it, but if there’s any doubt in your mind I’m happy to provide you with more information, help you with (simple) calculations and upload some sketches of how it could be done.

[glenann]

I'd be looking to incorporate a 50mm gap / cavity. The reason for this, would be to allow better air movement to help the building dry out and to avoid stagnant damp air build up. I know this will reduce the internal dimension, but in my opinion it's a sacrifice worth making. Further to this, if not already present, I'd retrofit weep vents one brick above ground level in the existing brick work. This is very cheap and simple, all you need to do is drill out the existing mortar and slide the vent in with a bit of flesh mortar to point it into place. Not only will this give the internal moisture somewhere to escape, it will aid air movement through the cavity.

Can I take it that as you're installing a breather membrane (a very good idea, I'd recommend using a reflective material) you'll be fabricating the panels and installing them as a freestanding structure within the building?

For so many reasons I'm not going to go into if you’re really not interested, I’d strongly recommend you reconsider a concrete floor. If it’s cost related, based on your original 16’ x 9’ dimensions the material cost (including 100mm insulation) would be approximately £1000. If you can operate a shovel, lift a full bucket and drive a wheelbarrow you could do it yourself comfortably in a weekend, or in a day if you don’t mind getting a sweat on! Two experience workers could easily do this in a day and would charge you ~£150 each, or you could get the insulation in and get a barrowed concrete service.
I estimate a timber floor would be a little over half the material cost so appreciate the implication, but you will overcome so many potential problem (this is why <90% houses are built this way) and have a better sounding floor that will last longer than the building it been poured in.
If you’re just not interested then I’ll leave it there and stop banging on about it, but if there’s any doubt in your mind I’m happy to provide you with more information, help you with (simple) calculations and upload some sketches of how it could be done.

Mate, your information and help is very much appreciated, thank you! I'm learning so much as I go along. I'll certainly take on board the things you have suggested and try and implement as much as is possible/affordable.

Thanks again Darren

[glenann]

So as an update. After taking onboard some of the great comments on here, I'm bracing up my back and planning to lay concrete on top of the existing pad so as to level it. I always wanted to do it, but thought it was way more expensive than joists and chipboard. Talking to a builder friend, who uses someone.. 2m3 or thereabouts of concrete for £250 seems like a bargain to me!

After that's laid, I can start on building the actual walls etc. I'm also now going for double plasterboard. Because of width and cost constraints, I'm using 9.5mm standard, with 12.5 Acoustic on top, for the walls and ceiling. Hopefully that'll do the trick.. enough for my needs anyway.

Cheers

[glenann]

I'm also now going for double plasterboard. Because of width and cost constraints, I'm using 9.5mm standard, with 12.5 Acoustic on top, for the walls and ceiling. Hopefully that'll do the trick.. enough for my needs anyway.

Does anyone have thoughts about just fixing the plasterboard together in a staggered config. without anything in between, such as Green Glue? Mostly, online reviewers rave about the stuff, but it’s staggeringly expensive! Apart from Dennis Foley here

Any thoughts/ideas or alternatives?

[sjs]

For over 20 years I have always specified non-setting mastic for sealing plaster board joints, corners etc, so a long time before anybody decided to upsell it by re-labelling it as something magic ;-)

Best of luck

[struth]

For over 20 years I have always specified non-setting mastic for sealing plaster board joints, corners etc, so a long time before anybody decided to upsell it by re-labelling it as something magic ;-)

Best of luck

used to use that in caravans