Building a Shoffice/Garden Room - value engineering it
Discussion
Inkyfingers said:
trickywoo said:
You’ll see no benefit of 100mm celotex in the floor.
25 is more than good enough.
It's true that the first insulation you add will be the most effective, but untrue to say there is no benefit in adding more. There is a reason why building regulations specify U-Values for floors, walls, roofs, glazing etc, it saves money in the long term and, more importantly, increases comfort.25 is more than good enough.
For a summer house it may not be worth it, but for a building you could potentially be spending 40+ hours a week in, at all different times of the year, insulating it properly is a no-brainer. It's much better to spend a few quid extra and do it properly from the start, than have to refit more insulation later or put up with a workspace where you have to wear two pairs of socks to stop them going numb!
I've got 25mm celotex in the floor and 50 in the walls and roof. I can be in it with snow on the roof in a t shirt thinking about opening a window.
100mm is a waste in a shed with practically no thermal mass. We aren't talking about big brick built structures here.
Pheo said:
Tin Hat said:
I would avoid EPDM roofs, we stopped installing them about 3 years ago, they are problematic. Kemperol is relatively inexpensive and significantly more reliable.
I have built our room with the deck directly over 100mm celotex, using foil back plasterboard beneath the joists as a token vapour barrier. I personally think that the cold/warm roof dilemma is not the drama that it could be in a garden room environment, as opposed to a living space that may have bathrooms and kitchens where significant moisture is generated.
I would definitely use celotex in the walls.
Cement board can be very effective for cladding, it is highly stable and durable and can often react well to being painted, requiring little long term maintenance.
Buy timber from a reputable timber merchant, if you use general Building goods suppliers, you’ll find 20% is unusable due to twist or warp.
Are you able to give a bit more detail on the roof makeup you're talking about? Not 100% sure I understand the makeup you're talking about?I have built our room with the deck directly over 100mm celotex, using foil back plasterboard beneath the joists as a token vapour barrier. I personally think that the cold/warm roof dilemma is not the drama that it could be in a garden room environment, as opposed to a living space that may have bathrooms and kitchens where significant moisture is generated.
I would definitely use celotex in the walls.
Cement board can be very effective for cladding, it is highly stable and durable and can often react well to being painted, requiring little long term maintenance.
Buy timber from a reputable timber merchant, if you use general Building goods suppliers, you’ll find 20% is unusable due to twist or warp.
Will look into the alternative roof products, and the cement board.
mikeiow said:
Tin Hat said:
I would avoid EPDM roofs, we stopped installing them about 3 years ago, they are problematic. Kemperol is relatively inexpensive and significantly more reliable.
(snip)
Just a side question: I’m curious what problems you have had with EPDM....we’ve recently done a 13’ x 5’ storage shed with it, went on a treat, I have high hopes it will outlast me!(snip)
For a shed, it would probably be fine - in essence, they are just large sheets of tyre inner tube.
When used in other applications, they are extremely susceptible to puncture, this can be nigh on impossible to locate, although EPDM installers do have methods of testing the membrane ( in my experience these tests also have mixed results ). We probably install about £500k of roof finishes yearly, historically EPDM generated around 95% of faults. It is interesting to note that high performance felt is frowned upon ( EPDM was sold as the solution to older flat roof systems),but in my experience is significantly more reliable!
thebraketester said:
Factor in a split ac. If you want to be comfortable all year round.
Not necessary at all, providing you take steps to effectively insulate the building and avoid heat build-up from prolonged direct sunlight through windows.Edited by thebraketester on Tuesday 14th July 14:01
I’m in the process of building one, I don’t have a huge budget and have been fortunate enough to pick up windows and doors in great condition for very little. eBay or Facebook marketplace are great for those if you are prepared to wait for the right thing to come up or travel a bit to go and collect.
Insulation wise, I’ve gone with 50mm PIR in the floor and ceiling and 100mm wool in the walls.
Still got to decide on the cladding and I am waiting for some french doors to come out of a property at the end of the month.
I can probably upload some pics as I have been taking some of the progress at various stages.
Insulation wise, I’ve gone with 50mm PIR in the floor and ceiling and 100mm wool in the walls.
Still got to decide on the cladding and I am waiting for some french doors to come out of a property at the end of the month.
I can probably upload some pics as I have been taking some of the progress at various stages.
thebraketester said:
Factor in a split ac. If you want to be comfortable all year round.
Pretty cheap for small units and will heat as well (although I am not sure how economically). Most work on wifi so if one were to be in range, or run an extender from the house along with power, you can make sure your office room is at the right temperature before you go to it...Edited by thebraketester on Tuesday 14th July 14:01
Harry Flashman said:
thebraketester said:
Factor in a split ac. If you want to be comfortable all year round.
Pretty cheap for small units and will heat as well (although I am not sure how economically). Most work on wifi so if one were to be in range, or run an extender from the house along with power, you can make sure your office room is at the right temperature before you go to it...Edited by thebraketester on Tuesday 14th July 14:01
The heating on them is actually very economical as it draws the heat out of the external air.
Tin Hat said:
Assuming that you are aware of cold/warm roofs and their differing ways of dealing with condensation, you may recognise that you either ventilate ( which increases the thickness of the roof ) or you need to (strictly speaking) develop an airtight box with vapour control layers. My suggestion avoids obsessing about the integrity of the VC layer, the internet would have you believe that this will lead to catastrophe
Yeah, was that a cold roof construction? There is someone on youtube who does a hybrid where he does cold roof but with the PIR hard up against the deck, and then Vapour Barrier layer across the joists. Isn't strictly compliant as he doesn't then ventilate the eaves, but works on the assumption that there isn't a lot of ways for vapour to get in-between, and as you say, it is a garden room, so how far do you go in engineering it?Am considering wall mounted all in one AC as I can install that myself vs a split where I need an engineer.
So, from what people have said, considering:
1) putting 100mm of EPS in the floor vs PIR etc
2) Reconsidering cladding options (could have a go at through coloured rendering I suppose!)
I've worked from a garden out building for getting on for 8 years. It is a chalet style with c50mm thick walls. No insulation. There is rock wool in the roof. No insulation in the floor.
It's fine in the summer with the doors and windows open (once the sun hits in the afternoon) and for winter I have a cheap wood burner from Machine & Mart, which gets it toasty warm in minutes and then I'm down to a t-shirt pretty quickly.
Suppose what I'm saying is, if you can have a woodburner, then is all this insulation necessary? I do have an endless supply of free wood though.
I have never felt the need to up the insulation levels.
It's fine in the summer with the doors and windows open (once the sun hits in the afternoon) and for winter I have a cheap wood burner from Machine & Mart, which gets it toasty warm in minutes and then I'm down to a t-shirt pretty quickly.
Suppose what I'm saying is, if you can have a woodburner, then is all this insulation necessary? I do have an endless supply of free wood though.
I have never felt the need to up the insulation levels.
alfabeat said:
I've worked from a garden out building for getting on for 8 years. It is a chalet style with c50mm thick walls. No insulation. There is rock wool in the roof. No insulation in the floor.
It's fine in the summer with the doors and windows open (once the sun hits in the afternoon) and for winter I have a cheap wood burner from Machine & Mart, which gets it toasty warm in minutes and then I'm down to a t-shirt pretty quickly.
Suppose what I'm saying is, if you can have a woodburner, then is all this insulation necessary? I do have an endless supply of free wood though.
I have never felt the need to up the insulation levels.
I don't have an endless supply of free wood, and I'm in a built up area. Worth considering a fire but I suspect the sunk cost is probably quite high before payback, if at all when you are buying wood in.It's fine in the summer with the doors and windows open (once the sun hits in the afternoon) and for winter I have a cheap wood burner from Machine & Mart, which gets it toasty warm in minutes and then I'm down to a t-shirt pretty quickly.
Suppose what I'm saying is, if you can have a woodburner, then is all this insulation necessary? I do have an endless supply of free wood though.
I have never felt the need to up the insulation levels.
I'm actually, to be honest, more worried about thermal gain in the summer than I am heating int he winter, I think. The location would be in full sun from midday through till 7pm, so it is going to get a fair amount of sun (hence Equus point about cladding colours being a worry!)
I built a cabin from Tuin last summer and use it pretty much everyday.
The walls are 44mm thick - with no insulation. I believe with the windows the walls were the least concern for heat loss.
I insulated the floor with 40mm celotex, above which is 18mm ply and the floorboards.
I thought this would be good enough but it was COLD in the winter. Even with a 3kW oil heater it was cold.
I have since insulated the roof with 100mm celotex between the purlins. I used expanding foam to minimise voids and prevent condensation problems. Then installed plasterboard beneath the insulation board.
The difference is night and day, very toasty in cold conditions with the heater just coming on periodically. I have no plans to insulate the walls as it is unnecessary. Most heat will be lost through the roof so concentrate your efforts there.
The walls are 44mm thick - with no insulation. I believe with the windows the walls were the least concern for heat loss.
I insulated the floor with 40mm celotex, above which is 18mm ply and the floorboards.
I thought this would be good enough but it was COLD in the winter. Even with a 3kW oil heater it was cold.
I have since insulated the roof with 100mm celotex between the purlins. I used expanding foam to minimise voids and prevent condensation problems. Then installed plasterboard beneath the insulation board.
The difference is night and day, very toasty in cold conditions with the heater just coming on periodically. I have no plans to insulate the walls as it is unnecessary. Most heat will be lost through the roof so concentrate your efforts there.
Joelonghair said:
I built a cabin from Tuin last summer and use it pretty much everyday.
The walls are 44mm thick - with no insulation. I believe with the windows the walls were the least concern for heat loss.
I insulated the floor with 40mm celotex, above which is 18mm ply and the floorboards.
I thought this would be good enough but it was COLD in the winter. Even with a 3kW oil heater it was cold.
I have since insulated the roof with 100mm celotex between the purlins. I used expanding foam to minimise voids and prevent condensation problems. Then installed plasterboard beneath the insulation board.
The difference is night and day, very toasty in cold conditions with the heater just coming on periodically. I have no plans to insulate the walls as it is unnecessary. Most heat will be lost through the roof so concentrate your efforts there.
all these years builders have had it wrong?The walls are 44mm thick - with no insulation. I believe with the windows the walls were the least concern for heat loss.
I insulated the floor with 40mm celotex, above which is 18mm ply and the floorboards.
I thought this would be good enough but it was COLD in the winter. Even with a 3kW oil heater it was cold.
I have since insulated the roof with 100mm celotex between the purlins. I used expanding foam to minimise voids and prevent condensation problems. Then installed plasterboard beneath the insulation board.
The difference is night and day, very toasty in cold conditions with the heater just coming on periodically. I have no plans to insulate the walls as it is unnecessary. Most heat will be lost through the roof so concentrate your efforts there.
Interesting debate in terms of insulation. I understand the roof being the most important bit - the importance of loft insulation is pretty indicative here. I have always lived in houses with uninsulated walls, but putting stuff into ceilings has been very effective.
My lean-to garage, all wood, no insulation, gets very cold in winter and very hot in summer. I have to take that as the best indicator for how a similarly constructed building would behave in the garden.
I think if/when we do it, there will be insulation everywhere to keep heat in in winter, a roof velux (with blind) to vent hot air, doors and windows on more than one side of the building in order to allow airflow, and most likely an aircon unit for both heating and cooling.
Not really a budget build, but if the room will get serious use, I suspect worth it. Still way cheaper than doing an extension, and probably slightly value additive to the house if using man maths.
We have a study already, but would quite like another workspace, and a small gym.
My lean-to garage, all wood, no insulation, gets very cold in winter and very hot in summer. I have to take that as the best indicator for how a similarly constructed building would behave in the garden.
I think if/when we do it, there will be insulation everywhere to keep heat in in winter, a roof velux (with blind) to vent hot air, doors and windows on more than one side of the building in order to allow airflow, and most likely an aircon unit for both heating and cooling.
Not really a budget build, but if the room will get serious use, I suspect worth it. Still way cheaper than doing an extension, and probably slightly value additive to the house if using man maths.
We have a study already, but would quite like another workspace, and a small gym.
Harry Flashman said:
Interesting debate in terms of insulation. I understand the roof being the most important bit - the importance of loft insulation is pretty indicative here. I have always lived in houses with uninsulated walls, but putting stuff into ceilings has been very effective.
My lean-to garage, all wood, no insulation, gets very cold in winter and very hot in summer. I have to take that as the best indicator for how a similarly constructed building would behave in the garden.
I think if/when we do it, there will be insulation everywhere to keep heat in in winter, a roof velux (with blind) to vent hot air, doors and windows on more than one side of the building in order to allow airflow, and most likely an aircon unit for both heating and cooling.
Not really a budget build, but if the room will get serious use, I suspect worth it. Still way cheaper than doing an extension, and probably slightly value additive to the house if using man maths.
We have a study already, but would quite like another workspace, and a small gym.
I was going to say don’t you live in a 6 bed pile with only the three of you! But like me you do love a good project My lean-to garage, all wood, no insulation, gets very cold in winter and very hot in summer. I have to take that as the best indicator for how a similarly constructed building would behave in the garden.
I think if/when we do it, there will be insulation everywhere to keep heat in in winter, a roof velux (with blind) to vent hot air, doors and windows on more than one side of the building in order to allow airflow, and most likely an aircon unit for both heating and cooling.
Not really a budget build, but if the room will get serious use, I suspect worth it. Still way cheaper than doing an extension, and probably slightly value additive to the house if using man maths.
We have a study already, but would quite like another workspace, and a small gym.
I agree using as much insulation as possible is good, but it is a hard call to know where you could shave a bit of cost off and not really notice (or the payback period is many many years). For example diminishing returns on loft insulation - I think I’ve read the first 100mm saves you the oft quoted £100+ a year, the extra 170mm to make a compliant 270mm total is like £20.
It’s occurred to me that as my plan is to split the place in two, with one half a shed / workshop type space, I could insulate that bit with EPS, and insulate the internal wall similarly, again to reduce the cost as the EPS is so much cheaper. Worth thinking about. Although detailing the wall to ensure two different spaces would be a challenge without bridging the insulation badly.
Harry Flashman said:
Interesting debate in terms of insulation. I understand the roof being the most important bit - the importance of loft insulation is pretty indicative here. I have always lived in houses with uninsulated walls, but putting stuff into ceilings has been very effective.
However, most UK houses are a double skin of brick/block with a cavity in between - whereas typical UK roof construction is a single plasterboard ceiling - a big open draughty void and some tiles on top.Not hard to see why some insulation above the plasterboard is a good place to start......
I think the numbers quoted more widely are still that 25% of heat loss is through the roof & 35% through the walls - but that's a total and not proportional to the surface area. So there highest concentration of loss is through the roof (heat rises) but the highest absolute level is through the walls.
Pheo said:
I was going to say don’t you live in a 6 bed pile with only the three of you! But like me you do love a good project
Yes, well, um...yeah. This is basically because my pregnant wife has banned me from tinkering with the house any more. I mentioned doing an extension and she mentioned kicking my arse.
My excuse is that we have another Flash mini on the way, and we'll be overcrowded. I think we all know that this is complete rubbish and that the real reason is exactly as you say...
Edited by Harry Flashman on Wednesday 15th July 22:25
I'm in the process of converting my garage 4m x 2.8m (so too small for anything other than the Caterham). Double hipped tiled roof, single skin brick walls and a cracked to buggery concrete floor.
I've done it myself and not on the cheap, but for insulation I used Recticel:
Floor: 70mm between new timber floor
Walls: 50mm between studs, overlaid with 25mm
Roof: 100mm overlaid with 25mm
The insulation and tape cost £608 delivered including VAT from these guys and I got it the next week in peak lockdown: https://www.insulationexpress.co.uk/
The above spec is generally compliant with resi U values. As has been said elsewhere, spending several grand on a building you can't use for 4 months during the winter doesn't seem to make much sense for the sake of a few extra hundred £ on insulation.
It did however take me three weeks, THREE weeks to install it - compound cuts on a hipped roof is not easy!
url]
|https://thumbsnap.com/Msvn7c9N[/url]
I've done it myself and not on the cheap, but for insulation I used Recticel:
Floor: 70mm between new timber floor
Walls: 50mm between studs, overlaid with 25mm
Roof: 100mm overlaid with 25mm
The insulation and tape cost £608 delivered including VAT from these guys and I got it the next week in peak lockdown: https://www.insulationexpress.co.uk/
The above spec is generally compliant with resi U values. As has been said elsewhere, spending several grand on a building you can't use for 4 months during the winter doesn't seem to make much sense for the sake of a few extra hundred £ on insulation.
It did however take me three weeks, THREE weeks to install it - compound cuts on a hipped roof is not easy!
url]
|https://thumbsnap.com/Msvn7c9N[/url]Harry Flashman said:
Pheo said:
I was going to say don’t you live in a 6 bed pile with only the three of you! But like me you do love a good project
Yes, well, um...yeah. This is basically because my pregnant wife has banned me from tinkering with the house any more. I mentioned extension and she mentioned kicking my arse.
My excuse is that we have another Flash mini in the way, and we'll be overcrowded. I think we all know that the real reason is exactly as you say...
]
(& you know she's right.......
Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff