Building a Shoffice/Garden Room - value engineering it

[Milsey]

Pheo said:

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.

Ours is approximately 6.5m x 3m, 1/3 is going to be storage and 2/3 garden room. You can feel it is warm, even with a 6 foot wide opening for the doors that are due to go in. We planned to be able to use this space all year round so may have to install a small heater for the colder months, warmer months we will have plenty of ventilation with two opening windows and french doors at the front. I estimate the total for insulation and foil tape etc to be around £350.

If you want a full sized sheet of 50mm PIR I have one left over going cheap!

[BaronVonVaderham]

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.

Good to know, very useful and timely post for me. The OP’s, and other posters seemingly over-engineered approaches were starting to have me concerned that I’d rather under-engineered.

We have just finished building a Tuin log cabin with the aim of using it all year round as an office.

So far we have 25mm EPS in the floor, 18mm t&g spruce floorboard with carpet on top.

Will now make plans for insulating the roof!

[Joelonghair]

bobtail4x4 said:

all these years builders have had it wrong?

Builders of what and wrong about what exactly?

The roof of my cabin is much thinner than the walls (18mm single T&G vs 45mm double T&G) and is an apex roof so a large surface area. Insulating it made a huge difference.

Yes insulating the walls would also reduce heat loss, but not by as big of a margin as the roof. I have a large double door and two windows either side that I obviously couldn't insulate. There is also the additional cost vs reward to consider, a reduction in inside space in an already small structure (5x3m), and I like the aesthetics of the timber walls.

In a framed structure then yes you would have to insulate the walls. But in a structure like mine it is unnecessary when you can be kept toasty in deep winter with a small heater costing pennies.

[bobtail4x4]

with insulated walls your heater would be off more than its on,

it was this comment of yours,

"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."

[lost in espace]

Youtube William Griffin has an interesting system, he documents it all with components.

https://www.youtube.com/channel/UChqWFbSX8STP_c8W0...

[Pheo]

Milsey said:

Ours is approximately 6.5m x 3m, 1/3 is going to be storage and 2/3 garden room. You can feel it is warm, even with a 6 foot wide opening for the doors that are due to go in. We planned to be able to use this space all year round so may have to install a small heater for the colder months, warmer months we will have plenty of ventilation with two opening windows and french doors at the front. I estimate the total for insulation and foil tape etc to be around £350.

If you want a full sized sheet of 50mm PIR I have one left over going cheap!

Ah can you come build mine?

So you went for rockwool in the walls? Any particular reason?

@ Harry - Congrats, we've got a now 8 month old who is the reason I need a new office as she stole mine (rude) as we don't live in a 6 bed (but I do now have a british racing green painted dining room, which is partially your fault )

I've been watching williams video's on YouTube extensively; I think he makes some really sensible accommodations to it being a garden room (lets be practical, is it a 100 year building? probably not). And can't argue with the look of the product at the end. His piling system is also clever.

[Milsey]

To be honest, I had almost 2 full rolls of rockwool left over from insulating the loft a few years back. I knew they would come in handy one day.

I’ve been trying to keep the costs manageable so having these helped. It may not be as effective as the PIR insulation but it seems to be doing a good job at the moment.

[Joelonghair]

BaronVonVaderham said:

Good to know, very useful and timely post for me. The OP’s, and other posters seemingly over-engineered approaches were starting to have me concerned that I’d rather under-engineered.

We have just finished building a Tuin log cabin with the aim of using it all year round as an office.

So far we have 25mm EPS in the floor, 18mm t&g spruce floorboard with carpet on top.

Will now make plans for insulating the roof!

I love my Tuin cabin and sure you will too, but yes definitely insulate the roof before winter as otherwise it really is not pleasant. I found after the roof was insulated it was huge improvement. I had leftover 100mm Celotex PIR from an extension so used that, and given the difference it made I wouldn't go any thinner.