Garden office materials

[bolst3r]

I've decided with the house occupied by children that I need my office to be in the garden. The first part of this project is to look at prefab solutions then cost up building my own. I'm currently pulling together a spreadsheet of items necessary to reach the spec required and have a couple of questions.

A friend has a spare roll of cromar vent free however I was planning on using tyvek on the walls and roof, is cromar a comparable product and can it be used instead of tyvek?

Insulation wise I'm allowing the following:

All celotex

Floor: 25mm
Walls: 75mm in cavity 25mm covering all everything internally
Ceiling: 50mm

Does this sound about right? I assume celotex whilst expensive is really the only way to go

For the roof I initially thought about insulated pressed steel but feel the following would be just as good, cheaper and perhaps easier to install:

Tyvek or cromar over roof joists, 18mm wpb over membrane. 50mm celotex over wpb then epdm over the lot.

Using the materials above I believe I could create a sound well insulated environment that's 4x3m for about £3.5k as apposed to a comparable pre fab solution for £12k

Any experience or tips much appreciated

 

[ban-all-sheds]

You'd have to insulate it yourself, but Warwick Buildings workrooms are a lot better made than your average shed. Don't know how the total price would end up, but unless you're desperate for the fun of building your own, the difference would probably be too small to make it worth the aggro.

IME anything marketed as a "garden office" will be overpriced.

 

[bolst3r]

Thanks but unless I'm missing something those Warwick offices are £11k. I've seen the small 3x4m pinnacle on this site (http://greenretreats.co.uk/photo-gallery.html) which is what I've based my costs on - it's about 12k however with comparable products I can built it myself for £5k and I would have thought it would only take 2-3 weeks to construct. I already have the services in place and 3/4 of my hard standing (just need to add the extra area) and by reducing the quality of the cladding and going for an insulted rubber roof I can get the price down to around £3.6k so building it myself is a no brainier.

 

[ban-all-sheds]

Thanks but unless I'm missing something those Warwick offices are £11k.

You'd have to insulate it yourself, but Warwick Buildings workrooms are a lot better made than your average shed. ...

IME anything marketed as a "garden office" will be overpriced.

 

[ban-all-sheds]

The small 3x4m pinnacle on this site (http://greenretreats.co.uk/photo-gallery.html)

Can't get the full sized images to load, but they look like they have a huge amount of glass - you'd need aircon in the summer. And good security.

 

[ban-all-sheds]

Less garden-shed-like:

3 x 5.1m, £3.5K.




From memory Lugarde might also be worth checking out.

 

[bolst3r]

Ah, I see the sort of thing you mean, I called Warwick about garden offices and they quoted me £9k but this one you've sent through is much cheaper as you say... Only thing is, by the time it's insulted (floor, ceiling, walls) plaster boarded, skimmed and painted it I will be adding another £1.5 as it will have to be studded and vapour barrier installed. My initial thought was to buy a decent summer house as the outer then put the other necessary bits inside but there's no real saving from what I can see doing it that way.

Will check out that other company you suggest.

Know what you mean about all the glass making it hot but figure decent foil backed PIR not only keeps things warm in the winter but cooler in the summer, this mixed with decent spec glazing it should be ok, or am I living in cloud cookoo land?

 

[ban-all-sheds]

The photo is of a Lillevilla log cabin.

I would have thought that foil-backed PIR would do an excellent job of trapping the heat from solar gain inside the building

But then an ASHP could be the best way to heat the place anyway.


Don't suppose you've got your own lake and £75K to spare?

http://floating-offices.co.uk/

 

[bolst3r]

Wow £75k that's some office shame i'm only short £70k and a lake...

I do like trying to build my own stuff rather than paying an over inflated price... Built this (see below) to save a few £k and really fancy doing the garden office but I work @ home full time so the thing I build has to be suitable.

Can't work out if you're mocking the foil back PIR suggestion or do actually think it will stop the solar gain... Haven't even thought how I would heat it but figured if it's really well insulated then a small oil heater on for an hour in the morning might be enough to get it to a decent temperature. Or am I way off the mark?

Untitled

• bolst3r
• 7 Jun 2013
• 3

 

[ntb]

Insulation wise I'm allowing the following:

All celotex

Floor: 25mm
Walls: 75mm in cavity 25mm covering all everything internally
Ceiling: 50mm

Does this sound about right? I assume celotex whilst expensive is really the only way to go

You will get better performance from a given amount of money spent on insulation if you put more in the roof and less in the walls. Heat rises.

Celotex is great where space is limited but is not economic where it isn't e.g. loft insulation. Polystyrene or rockwool batts would be fine in your instance unless damp is an issue.

 

[ban-all-sheds]

Can't work out if you're mocking the foil back PIR suggestion

No - you deffo need it to be well insulated.

or do actually think it will stop the solar gain... Haven't even thought how I would heat it but figured if it's really well insulated then a small oil heater on for an hour in the morning might be enough to get it to a decent temperature. Or am I way off the mark?

I thought you were planning to have a lot of glazing?

That's where you'll get the solar gain, and if the building is well insulated it will get hot inside.

 

[bolst3r]

it's a balancing act with light, heating and solar gain. I'm planning on a single door which will be mainly glazed, a row of three windows (70x70mm) and another single window which compared to most new 'garden offices' is quite restrained.

I believe by using foil backed celotex i'll be able to avoid a lot of solar gain from heat bridging the insulation however i'll still have the sunlight heating up the office via the windows but each will have a blind so hopefully this will help somewhat.

Happy to put rockwool bats in ceiling void if i'm forced down the cold deck route however I do worry about the lack of foil backed on the roof as I feel this could contribute towards the oven effect. How are you meant to stop the suns rays passing through the roof without this?