Garage conversion - building advise needed

[Rob100]

Hi all,

I am in the initial stages of planning my garage conversion, I will start a tread when the time comes, but for now I'm just trying get a few building issues clear in my own mind. I am not a builder, but feel happy I can do the job (well maybe not the plastering - this is the only unknown) with some pointers.

Other than doing lots of drawings of proposed layouts, I'm currently laying a base for a shed (so we can clear all the "rubbish" out of the garage) and having the consumer unit moved to another wall as I don't want it in the "cinema room".

As I've read in other posts an effective method of sound insulation is to build a stud wall (2"x4" timbers) 1" from the brickwall, fill with rockwool and cover with 2 layers (1 x 12mm and 1 x 16mm) plasterboard.

1) Should the rockwool be allowed to touch the brick wall? Should it touch the brick wall? If it shouldn't, how do I stop it?

2) I am leaving the up and over doors in place, but removing the runners etc. I will then screw them up, so they could not be opened even if you tried. I had then planned to cover the rear of the doors (to the framework with a plastic sheet) to prevent rain etc getting in. I then wanted to do a double thickness wall. Would I be best building a block wall inside the doors and then a stud wall inside that or shall I build two stud walls (the outer one somehow having a "back" to it) with a 1" gap between? Which will give the best thermal and accoustic insulation? If I go for the two stud wall method, should I use plasterboard on the wall inside the doors (the outer one) or should I use chipboard, OSB, plywood etc?

3) Vapour barriers - should I have one on the walls? If so where does it go? Does foil backed plasterboard do the same thing or is that for thermal insulation? If I use foil backed plasterboard, I'm assuming the foil side faces the rockwool?

4) Floor - This is a concrete floor and there is already a DPC. My plan is to put down some 2"x2" timers, fill with rockwool or 2" insulation slabs and then chipboard over the top. I will have to "pack up" (as I head towards the double doors) as there is a slight slope. Does this sound okay? If so, what thickness chipboard?

5) Downlighters in roof? Obviously I plan to inulate the roof and probably board the other side, however I've been reading that you need a segregated ceiling void or firehoods on downlighters? Is it not okay for the downlighters to touch the rockwool? Is this a fire hazard?

I will probably have more questions, but if I get answers to these that will be a great start.

Thanks in advance.

Rob.

[Paul_T]

Hi mate - I'm an Architectural Technician, hopefully I can clear a few things up for you but will probably generate more questions than answers!

You're best having a chat with your local Planning Department at the council, you might not need planning permission you're best asking now to be on the safe side, you'll probably be allowed to block up the garage door opening with brickwork / blockwork & render as this will be the only thing Planning will be interested in. One thing you'll definately need is Building Regulations Approval as you converting the garage into a habitable room so you'll have to make it watertight (as I'm sure you'll want it to be) and nice and cosy in winter.

I'm assuming the garage is joined to the house so this is how I would go about converting it. Brick the garage door up to form your outer leaf (if it's only single storey you should be ok building straight off the concrete floor. The inner leaf I'd construct in timber frame (say 75mm x 50mm studs) like you suggested - but you'd need to keep it approx 50mm off the face of the outer leaf. Your vapour barrier would be between the outer leaf and the timber studs (to stop the insulation getting any moisture in it). pack the studs out in mineral wool insulation then put a breather membrane on top followed by the plasterboard sheets and a skim finish. There are lots of horror stories about timber frame constructions but they're all to do with not being built right - if it's done correctly then they're brilliant at keeping the heat in (Scandinavians use 300mm thick of insulation and most of the houses are built that way). For the walls adjoining the house, you can insulating plasterboard on dabs (with a skim finish). The blockwork should be pretty good at sound deadening - where most sound transmittance occurs, it comes from gaps around doors frames especially the bottom - even those draught excluder brushes can be very effective as well as escutcheons over keyholes.

Bear in mind that most garage floors ar not flat - they're sloped slightly towards the door in case of petrol / oil spillages - this wouldn't be a huge problem though, you'd just need a small timber rail at one end to rest the floor joists (or whatever) on - then fill the spaces with the polystyrene insulation slabs - we need to specify 60mm these days in new homes to satisfy building regs, so you can see you wouldn't need a lot - then just top off with 19mm Weyroc floorboarding. You may want to consider having the new floor level with that of the house - but it might take away a bit of height from inside the new HT room, especially as the roof is where you'll need the most insulation.

For new homes now, we need to specify 250mm of mineral wool insulation to get a "U" value of 0.16W/M2K (if that means anything to you) there are thinner alternatives but "thinner" usually means "dearer" too. Have a Look at the website of a insulation firm called Celotex - they tend to specialise in thin solutions that don't cost the earth and are usually easily available from most builders merchants.

PS - Rockwool isn't combustible - we also use it in floors to give fire protection in garages when there's a bedroom above so not much chance of it catching fire - but you're best checking with the manufacturer of the lights on that one as they'll probably need a ventilation space.

Hope it helps

Paul

[Johnny Thunder]

The problem you will have with insulation around halogen spotlights, is
overheating of the lamps. These halogen lamps tend to "go" quite often
anyway, and if there is no breathing space for them, they will not last
very long.
Fire retardant hoods are there for that purpose only, to stop fires. One
side effect of these hoods, is the lamp running at a hotter temp than
normally recommended, and therefore not lasting as long.
I never install halogen spots where insulation is present.
I would recommend you have a rethink on the lighting Rob.

Johnny.

[Rob100]

Paul_T,

Thanks for the lenghty reply. You have cleared up a number of points, but as you say have generated a few more questions

Yes the garage is joined to the house, but due to the fact the house is "side-on" down a hill the garage floor is already 18" or so higher than the house so no chance of making it the same level and knocking a door through. However the rear door from the utility and the garage rear door are only a few feet away. At first I thought this was a pain, but the more I think about it it's not so bad as there's less chance of noise travelling.

but you'd need to keep it approx 50mm off the face of the outer leaf. Your vapour barrier would be between the outer leaf and the timber studs (to stop the insulation getting any moisture in it).

How would I attached the vapour barrier to the "rear" of the studs when I can't get round that side? Sorry if this is a stupid question. I'm sure I could find a way, but would like to know what the "normal" way is?

For the walls adjoining the house, you can insulating plasterboard on dabs (with a skim finish). The blockwork should be pretty good at sound deadening

I would rather build a timber stud frame away from the blocks and stick to the "room within a room" idea. It's only one more stud wall to build.

Thanks again,


Rob.

[Rob100]

Originally Posted by Johnny Thunder

I would recommend you have a rethink on the lighting Rob.

Johnny.

I'm not set on having downlighters. Sounds like it's more trouble than it's worth. I'll think again...

Thanks for the info.

Rob.

[Paul_T]

Hi Rob,

I think most stud partitions are built away from the wall and then put in place, so once the frame was built the vapour barrier would be fixed to the back and then the partition put in place.

In terms of lighting - you could always just use some wall lighters with regular bulbs - that way you could have a dimmer switch and I'm sure I've seen a controller somewhere that gradually dims the lights when the film starts...

[garyc]

Hi Rob,

I'm a senior Architectural Technician , lets start from scratch:-

- you are leaving the garage door in place - planning not interested

- building regs is required if you are planning to make this conversion a habitable room interms of selling the property. without building regs it has be classed as a 'bonus' room or store. choice is yours

- room in room timber construction is the way to go, you might want to consider using cls timber for your walls, with 63mm of 89mm thick. you will find its more uniform(straighter) than normal timber.

-the vapour barrier of the single skin outer brick wall can be easily done by using foil backed plasterboard on the inside of the timber frame wall. yes foil face goes against the insulation

-insulating between the studs can easily be done with 'friction fit' insulation which fits nice between the studs ie. rockwool flexi

-wall behind garage door you could do this with a double timber frame, plasterboard both sides with insulation between.

-floor to take out the garage fall, you could try fixing a timber plate to each side of the garage then using mini hangers span the floor joist (100 or 150mm deep) from side to side creating a timber suspened floor then, no messing around with packing etc. most garage floors do not have a dpm so for my money I would lay a dpm (plastic) sheet over the garage concrete floor and lap up the sides to dpc level. 18mm chipboard flooring should be ok. insulating the floor is cheaper to use a mineral wool (loft insulation) 150mm+ should achieve a good u-value. refer to www.rockwool.co.uk for info

I know you ask a simple question and you get lots of opinions

cheers

Gary

[Rob100]

Gary,

Thanks for the reply.

My plan always has been to build behind the doors and when we sell in the future (we only moved in a month ago, so it will be many years) I remove my room and convert back to a double garage. Also I'd rather nobody (neighbours, passers by etc) knew what was within. I know there are probably insurance issues, but that's my decision.

-the vapour barrier of the single skin outer brick wall can be easily done by using foil backed plasterboard on the inside of the timber frame wall. yes foil face goes against the insulation

So are you saying there's no need for a "backing" to the timber frame to prevent the rockwool from touching the brick wall?

-wall behind garage door you could do this with a double timber frame, plasterboard both sides with insulation between.

Are you suggesting to make a single wall that's approx 8" thick?

As for the floor I only have about 85mm from the concrete floor to the bottom of the rear door into the garage. I'll have to go for the 60mm timber and packing method. There is definately a DPC under the garage floor.

Thanks again,


Rob.

[garyc]

Originally Posted by Rob100

Gary,

So are you saying there's no need for a "backing" to the timber frame to prevent the rockwool from touching the brick wall?

Rob.

If you live in an exposed area and see driving rain coming through your brickwork and running down the inside of the garage then you may want to take extra measures. But leaving an air gap behind you timber studs and putting the rockwool inbetween will leave an airgap. The friction fit insulation will stay in place with nothing behind, basically thats how I'm doing mine, I am considering putting some cavity batt type insulation between the timber studs and outer brickwork for extra warmth, but not sure its necessary!!

what i did for the wall behind the garage door, was to build a timber frame using 63mm wide cls timber, but not screwed into place, lay it on the floor (rear side facing up - garage door side) screw plasterbaord to that side then lift into place. once screwed in then build a second timber frame and butt it upto the first, pack with insulation and finish with vapour check plasterboard. you could even put any cable ducts to the back of the wall for easy cabling etc.

I have tried to attach a pic of the how I put the floor in. Hopefully I worked. Again its just the way I decided on - trying not to use an blockwork (all DIY) and to make it easier by using an edge timber and mini hangers rather than trying to plug and screw each floor joist.

hope this helps

Gary

PS. sorry pic too big - could email if you are interested

[woody67]

Originally Posted by garyc

Hi Rob,

I'm a senior Architectural Technician , lets start from scratch:-

- you are leaving the garage door in place - planning not interested

-floor to take out the garage fall, you could try fixing a timber plate to each side of the garage then using mini hangers span the floor joist (100 or 150mm deep) from side to side creating a timber suspened floor then
I know you ask a simple question and you get lots of opinions

cheers

Gary

Not forgeting any condition on the original PP, or covenant on the property to prevent garage conversions? Then they will be interested as a parking space is being removed.

Also not forgeting that a suspended timber floor could potentially require ventilating?

************
If the garage door was sealed with clear silicone around it, then no moisture will get through. The whole of the back of the door could be covered with polythene to prevent interstitial condensation, then 100 rockwool placed against that, and then just a 75mm stud (with 50 rockwool) and 12mm plasterboard and skim.

There is no need for a double wall.

Also. I can't see Building control insisting on the door/new wall being insulated to the curent regs, as then this implies that the rest of the floor and other walls and ceilings will need insulating too. Around my local area, the BCOs just ask for "some" insulation behind the door.

[Paul_T]

If he decides to get Building Control involved then they would / should insist that the new room comply with the current legislation, even if it means upgrading the floor insulation.

It's doubtful that there'll be a covenant to stop a garage being converted - covenents are usually put in place to stop ANOTHER garage being built so (as an example) it wouldn't interfere with lines of sight on a nearby road.

Rob, you should be fine doing the conversion without Planning or Building Regs, but only IF, as Gary says, you decide to revert it back to garage when you sell - if you decide to keep it as it is when you sell, you can always do a retrospective application.

For a bit of extra protection from driving rain you could also use some of that paint repellant clear paint (just what it says on the tin) - but I don't suggest you use it as a replacement for a vapour barrier, more of a backup.

[Rob100]

Gary,

Definately no rain coming through the wall!

I have sent you e-mail asking to send pic.


Woody67,

No convenants on garage conversion. We have 2 gravel parking spaces out front and also plan to move a fence to give us one or two more some time in the future.

I want to make the front wall as thick as possible as I see this as being the weak point for sounds escaping, so will probably go for 2 x 2" + plasterboard walls.


Paul_T,

Would definately remove if we sold as I don't see losing a double garage to be a plus point in most people eyes.

Also doing it "officially" will cause problems with electrical wiring etc


Thanks for all the replies.

Rob.

[Rob100]

I made some enquiries with several local builders merchants and non of them stock Rockwool. Most tried to sell me Isowool and another Crownwool. I'm going to go to see one of them tomorrow.

Anyone used either of the above and in a position to advise how it compares to Rockwool?

Thanks,

Rob.

[woody67]

Rockwool is denser than fibreglass quilt, so has better sound absorbtion qualities. But you could get equal sound proofing by doubling or trebling the plasterboard, fitting Fermacell ( www.fermacell.co.uk ) boards, other fibre board or MDF, or a cork lining. Also your wall finish can help.

Don't assume that a thicker wall with lots of rockwool is going to be 'better'. The gains from a 100mm quilt and double board may be negligible in terms of sound escaping. ie there comes a point where the extra cost and work is not worth it. I can't do the calcs now, but if I've got time or can find my chart later tomorrow, then I can let you know.

[Rob100]

Originally Posted by woody67

Rockwool is denser than fibreglass quilt, so has better sound absorbtion qualities. But you could get equal sound proofing by doubling or trebling the plasterboard, fitting Fermacell ( www.fermacell.co.uk ) boards, other fibre board or MDF, or a cork lining. Also your wall finish can help.

Don't assume that a thicker wall with lots of rockwool is going to be 'better'. The gains from a 100mm quilt and double board may be negligible in terms of sound escaping. ie there comes a point where the extra cost and work is not worth it. I can't do the calcs now, but if I've got time or can find my chart later tomorrow, then I can let you know.

I had always planned on doubling the plasterboard. I could add a layer of MDF if that would help.

I did get one quote from an insulation specialist for Rockwool and it was double the price of the Isowool.

If you've got some calcs that would be a great help

Thanks,


Rob.