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New garage going up - things to remember before the builders start?


FridgeFreezer

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Don't know if you can still get it but years ago you used to be able to get products where you drill holes in the bricks and inject a substance that creates a damp course.

If you want any polystyrene for insulation I can give you some but it's got no u certificate or fire retardant so you'd have to do it after building inspector has been. I used it for my garage and it's great but I did cover it with wood to stop sparks melting it

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Robert - ASHP would be to warm (and optionally cool / dehumidify) the workshop, on the grounds they seem to be more efficient than something like old-fashioned electric, but it'd be quite a luxury item really. If memory serves, SimonR had one on his workshop which is what gave me the idea. In an ideal world I'd have the wood burner but it brings issues like flues and annoying the neighbourhood with smoke so far from perfect, even if it is cheap to run.

Lewis - I hear you on that, but I think screeds are quite a variable thing, a lot of commercial floors are screeded and are very tough but I don't know what the difference is. The end of the workshop that needs smoothing out is less likely to have vehicles jacked on it, and as it'll have the workbench & lathe it does want to be level. At the moment it's very standard garage/driveway tamped concrete finish so needs something, and I don't think epoxy floor paint would do it on its own.

Al - thanks for the offer, I'm going to have to think about insulation a bit more as just buying enough hardboard to cover the inside would add up to a fair bit (inside will be ~11m x ~3m x ~2.8m high).

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Ashp (day job here), great cop (coefficient of performance [simple terms - efficiency]) at higher external air temperatures but as the external temp drops off the cop goes poor also the units end up having less effective output because when they are in heating mode they need to go into a defrost cycle to keep the coil from freezing up, this means that during the defrost cycle the output goes to zero, the defrost can last (manuf dependant up to 10 mins) which does not sound a lot but it's nearly 20% of an hour.... Which means that the room starts to cool down before the next slug of heat is applied. I'm not saying they don't work or are somehow don't work, what I am saying is you need to be aware of the way they work and then consider a workaround....

The workaround I would suggest is don't select the heat pump heating output to match the heat loss from the garage (or your salesmans rule of thumb...) but go to the next size or two up, because what this means is the slug of heat available will be larger when in very cold conditions and when you want intermittent heating the space will heat up quicker... Why two sizes up from your initial heat loss calc or estimate well garages are leaky spaces to air change and what you are trying to do is heat the air above your setpoint temperature so that you can achieve your setpoint quicker. This in turn means that because of boyancy and air density between inside the building and outside the air will have a tendancy to leak through any gaps (garage door).

Once you have made the decision or commitment for the ashp the equipment cost of going to the next size up is actually not that great and it will modulate as all these days that I am aware of are inverter driven and therefore don't have high start currents and modulate their compressors to the load.

Ashp's when selected for cooling applications will normally provide much more heating than the space requires as the cooling load is the predominant load which means the derating and defrost time is less of an issue as you've got a bigger slug available for heating which far exceeds the heating requirement

(Sorry for the long post hopefully it's useful to you or someone else to consider the issues)

Rob

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Cheers Rob - one major difference is I only really need to take the "edge" off rather than attempt to heat a massive box to room temperature, the difference between working in ~3deg and working in ~10deg is massive, we found that even with a small wood burner in the lab (big cold space) it made enough difference to make working much nicer without needing to bring it up to "boiler thong" climate.

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If all you're trying to do is take the edge off the temp, then I don't think that economically a ASHP will be the best idea IMHO.

disclaimer for smart a!"£s: The following is a rough guess based upon zero assessment of the actual build listed above other than it will be leaky to air change + may or may not be insulated! Hence to anyone using these numbers please just alter them to your own needs and what you believe or calculate the numbers to be or if someone gives you specific seasonal COP's etc (note this is an intermittent heated application so a dwelling of office COP may not be "seasonal" in this application, etc etc .... just use it as a guide and make up you're own mind as to what you believe the numbers to be in your own head we are all big boys and responsible for our own decisions

At a guess the heatloss will be somewhere around 150W/m², this is the peak instantaneous heatloss estimate with the outside air temperature being about -4ºC and the internal temperature being 21º C, so the temp diff is 25º C, in simple terms, divide the 150/25 = 6W/m² per º C, so if you want about 10ºC internal temp, heatloss would be about 85W/m²

From the above post, the garage is about 10m long total, and although you've not listed the width (??) say 4m, thats 40m²

So the peak heating requirement is ~3400W to keep it at about 10 deg C, next question is how quick do you want to get it to that temp from cold (thermal capacity consideration), in simple terms, if you're looking for about an hours heatup and it's -4º to start with and it's a brick/ block internal face then you could need double this (~3.8kW) ....

Working on these numbers, get 2 x 3kW heaters and be done with it, and you'll have loads of spare change to pay for the loss of efficiency (given the electric heaters are 100% eff, and the heatpump will have an efficiency of maybe 3:1 (so the input energy would only be 1/3rd of the energy output, so you're electric cost would be 1/3rd of using an electric heater).

You also need to factor into this the amount of usage .... 3kW heater for 1 hr = 3kWh of electric use, if you use it for 3hrs per day, every day for say 1/2 of the year (allowing for a bit extra on weekends maybe, don't forget that the weather will be milder in autum and spring hence above 10 deg C so you may choose not to use the heating), that will be around 550 hours per year (worst case).

so at 3.4kW = approx 1900kWh / year

Have a look at your electric bill what you pay per kWh, we pay 12.44p/kWh, so annual cost at 3.4kW (1900kWh/yr) would be £240

using an ASHP will knock this down to about 1/3rd, so say £80. The saving is therefore £160/ year.

[not sure about this one.... not into house bashing air conditioning, and not sure how cheap they can be got, hence adjust the numbers according to a budget price you get) but lets say ... cost of ASHP installed (..... £3K (3.5kW ASHP), to maybe £3.8K (7kW)

So £3.5K / £160 saving = 19 year economic payback, to maybe 23 years

but the lifecycle of an an ASHP is about 10 to 15 years, say 20 if you're in the industry (either way it does not pay back).

hence save the cash and buy a couple of electric 3kW heaters...

If you really want or need cooling that's another matter...

Hope the above helps

Rob

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Radiant heating is always better in spaces that have high infiltration (air leakage) rates. Radiant heating covers quartz heaters too but not radiators (although they do have a fair % of heat by radiant means, most is by convection)

If the garage is connected to the house or only a short distance from the house I would be tempted to put a couple of triple panel rads in or some cheap double panel rads double stacked if wall space is a problem (weld the rad brackets for the front rad to the rear). You won't get 100% of the two rads output given you've blocked the radiant portion of the rear but it's a cheap low running cost permanent solution with a two stage thermostat (frost protection ... Stop the pipes freezing and a comfort setting, could just move the thermostat dial up and down as you'd require but I'd probably forget)

I use radiant gas in mine (3kw) but it is well insulated but has a roller shutter so the air change is still high enough for using gas in an internal space unflued for my needs plus an oil filled electric 2kw someone have me foc

Rob

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No problem , the main thing was just to give you an indication of the calc and then you can put your own numbers in and make an informed decision. If the installation costs are in the hundreds then the payback time improves, so too if your operating hours are longer.

(sorry did not want to come across a smart a$¥, or get shot down over something small)

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Great ideas all.....but may I be boring and suggest you think about door locks (5 lever mortice or level 10 security padlocks). Also, fit hinge bolts, so if some ne'er do well cuts your hinge pins the door will stay put.

Window locks are also a must, unless like me you never open them anyway, in which case just screw the transoms to the frame.

Choose your "exit" door and securely bolt the other one. If you have an "up & over" door, remember the locking system is little more than a latch and easily overcome. Fit bolts in the vertical door sides on the inside to secure the door in the "down position.

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Second the hinge bolts, cheap as chips and secures the hinge end of the door much better, this'll do it for cheap:

http://www.screwfix.com/p/hinge-bolts-steel-18-x-54mm/17201

If fitting windows, rather than screwing the sashes to the frame, just direct glaze them in with laminate glass, makes the window DIY-able, and much cheaper, and more glass area for a given opening!

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I'm going to put a sheet of polycarb over my windows when I get round to it....they're only single glazed timber frame units...it'll act as secondary glazing and if anyone should break the glass, hopefully they still won't be able to get in.

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Hinge bolts etc. are a good shout but the existing half of the garage already has uPVC double-glazed access door & a frosted window installed by the previous owners so they're reasonably secure. I'm considering bars or polycarb or similar across the window.

I did all those and more on the wooden inventing shed - bought an offcut of window security film from a local car tinters and backed all the windows with it, then screwed polycarb over the frame to "double glaze" it.

Main door looks like it will be insulated roller sectional type because it needs to be tall and can't swing out over the pavement - and it looks like insulated sectional is about the same price as anything else but has an excellent seal round it & 40mm thick foam core, mmm toasty! :D Getting a remote opener is quite reasonable and means no external handles/locks.

I'm also planning to concrete a length of tube into the floor at the entrance so I can lock a bollard or something in.

I realise nothing yet invented will stop a determined theif but all you can do is make life a bit harder than it's worth for most of them.

Will probably have some sort of CCTV too, what with that being my day job at the moment :D and probably an alarm of some description if I get round to it.

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Rob - You should write a post with some of those calculations & assumptions in for people building/insulating/heating a shed or workshop, I'm sure many would find it useful.

Ross - I have been taking pictures, but not had time to upload any. So far there's some foundations and a lot of mud!

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Thanks FridgeFreezer, I could have a go time permitting but it may be off topic, there is a wealth of useful bits on this forum it's just trying to find the info sometimes. Trying to finish off my plasma build and the lt230 which is in bits I really need to get my build done by sept (hence low profile)

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Thanks FridgeFreezer, I could have a go time permitting but it may be off topic, there is a wealth of useful bits on this forum it's just trying to find the info sometimes. Trying to finish off my plasma build and the lt230 which is in bits I really need to get my build done by sept (hence low profile)

I think its useful tech for anyone building a workshop or improving one!

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  • 1 month later...

Well the garage is almost finished the builders are almost finished, now the fun begins! I will upload some piccies and stuff at some point.

From the posts I guess you are talking brick walls.

My ultimate would be to stud them with wooden lathes/ infill with Cellotex insulation and nail plasterboard

I've been pondering this. Got my eye on job lots of slightly damaged insulation panels on eBlag, not sure if plasterboard is the right answer for a workshop? Will probably stick a couple of panels of OSB or ply up by the workbench to nail tools to, but that gets expensive doing it all the way round especially as the ceiling is ~2.8m so it's more than one board tall.

Definitely need to insulate the roof as the builders vented the fascia in anticipation so I've either gotta insulate it or freeze! :rolleyes:

Finally found some heavy duty indoor/outdoor screed to smooth the old floor, Cemex Cempolay Heavy Duty, will get the builders to throw that down on their way out.

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I've just found this thread and started reading it with one eye closed in case there was anything brilliant I hadn't thought of when I started my build - which was pretty much the same time as you by the look of it.

Luckily it seems I've thought of all the good stuff. Phew!!!

Mine is different though in that it's a drive extension and a new detached oak 'kit' garage.

Exciting times eh FridgeFreezer.

Have you thought about external lighting? I'm wondering about this now but haven't had any inspiration yet.

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I put down lighters all around the outside of my house. They only have 5w led lamps in but give plenty of light for walking around without falling over stuff, getting keys in locks etc as they're not in your eyes like lights that shine outwards. I have them on a combination of a dusk to dawn and an immersion timer, they come on at dark, off at 1am, on at 5 am and off again at dawn. Not sure if it's worth it though as they're only 30 watts total?

For outside working I have an led floodlight but obviously they cast huge shadows and blind you when they look at them so are of limited use.

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Got a PIR flood on the outside of the garage and side of house and a normal light on the back of the house so all covered there, nothing exciting.

Best money I spent was a dusk-to-dawn PIR lamp just inside the garage, so when you stumble in in the dark looking for the light switch, it comes on.

Floor is now screeded, as the plasterer was hanging round having done the kitchen I got him to do it, got a lovely finish and it only took him a couple of hours (gawd knows how much mess & trouble I could've made doing it myself). Time will tell how heavy-duty it really is.

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