Insulated Concrete Slab Garden Office - Questions

[Nickfromwales]

7 minutes ago, Ticky said:

Wouldn’t this prevent me from levelling the concrete? Unless it was ‘added’ after the shuttering was removed. 

 

😂😂 Just a guess. What size would be suitable? 

12mm / 14mm max at 450 o/c..

 

You can add the extra after the slab has cured. Just use Illbruck 330 foam or some EPS adhesive, bonding to both the existing insulation and the side of the 100mm soleplate.

May be a good idea to incorporate one linear run of 1/2" rebar right around the  perimeter. Steel is cheap enough. It's enough to drive you mad when you stare at these drawings for long enough!

[Ticky]

Thanks all

 

Another thing I'm not so comfortable with is that layer of pea shingle.

I'd feel better if it was a layer that would compact better so could I use gravel as long as it has no fines?

Would that be a problem?

 

Tree stumps completely out now so can start leveling the area finally!!

[Nickfromwales]

Pea shingle is fine tbh, just throw the first sheet of EPS down carefully and use that as a walking board to lay the rest, eg without disturbing the rest of the levelled shingle. I'll be making up a straight edge and some perimeter timbers as a slide, to level this in minutes. If this isn't right, the whole thing is fecked so I'll be going to town getting the shingle level / flat etc.

Maybe use gravel first, then just have a 50mm layer of pea shingle so levelling is a breeze. Bollocks to whacking / compacting layers of stone. It's a shed, and it'll be the best damn shed for miles! The beauty of a raft is that it doesn't need to be absolutely perfect underneath, unless it's taking a 2 or 3 storey 5 bed house that is. The steel in the concrete deals with any minimal depressions / voids that happen over the next few years from settlement.

 

If I carry on designing this any more, they'll be holding my fecking wake in it!!

[Ticky]

For the french drain would I be good allowing for approx 100/120mm around the perimeter? I'm thinking 60mm PVC pipe and enough room to surround it with pea shingle?

Do I need to worry about the back of the Room which will be up against the neighbours fence (and have the guttering) would I just feed that gutter into the f-drain?

 

Also, can I terminate the french drain into another part of the garden as I don't think i can route it to my existing rain water drain of the house. 

 

 

Edited May 9, 2023 by Ticky

[Ticky]

Ok, think I'm gonna use a soakaway for the above. Seems like a reasonable option

 

I'm about to order my insulated roofing panels today. Been speaking to a guy at ColourCladProfiles and they seem to have the best price and include all the guttering/fascias etc.

 

Plus there's a Coronation discount (that ends today) that knocks off the price of the delivery which'll save me £180

 

I know I don't even have the concrete poured yet but it's a 6 week wait on delivery anyway

 

Hope you're all good

Edited May 12, 2023 by Ticky

[FozzieKev]

I realise this was a year ago, loving all the detail that was given. Just wondered how people dealt with the thresholds, especially if anyone had put in bifolds and how they sat them on the raft? I was looking at VuFold but they seem to want the frames sat at a maximum of 5-10mm from the front of the “brickwork” (Even our house ones (another brand) are 30mm back), which then means the outer EPS presumably would be load bearing?

 

 

With bottom hung bifold did anyone put in a strip of Armatherm/CompacFoam/Other or is that simply far too much hassle and overkill?

[IanR]

I'm not sure that too many people are putting insulated rafts/slabs under garden rooms, but I and others were happy to give suggestions to the OP who wished to.

 

The perimeter EPS Upstand wouldn't be robust enough to directly take the loads of a Bi-Fold. When the doors are opened there are lateral loads being applied and I'd expect the upstand to move away the raft/slab. You're also not going to achieve robust fixings through the frame into the EPS, they're just going to pull out.

 

There are a number of ways of achieving it, as there's plenty of Bi-Folds and other thresholds on insulated rafts in houses, but there's more detailing required. 

 

Are you putting UFH into the floor? If not, do you really see any benefit in using an insulated raft? Or are you just happy to experiment?

If your set on using an insulated raft then post up what your thinking regarding your floor build-up and wall construction and I'm sure there will be a few suggestions on how to incorporate a Bi-Fold threshold.

Edited June 19 by IanR

[garrymartin]

1 minute ago, IanR said:

I'm not sure that too many people are putting insulated rafts/slabs under garden rooms

 

Never let me be accused of not bucking a trend... 😉

 

I put in an insulated slab without UFH, but there are no load-bearing structures on it. The superstructure sat on strip foundations / blocks / bricks and the bifolds sat on strip foundations / blocks. See the attached for info, but feel free to ask any further questions. This was 7 years ago, and I'm not saying I'd do it exactly the same again, but I've been very happy with it and even in the winter, the tiled floor remains a reasonable temperature. Zero issues.

 

[garrymartin]

[garrymartin]

[garrymartin]

[garrymartin]

[IanR]

5 minutes ago, garrymartin said:

Never let me be accused of not bucking a trend... 

 

But what you've done there is more typical, I'm assuming the recent poster has chosen this thread for the insulated raft, which does take the load bearing walls.

[garrymartin]

1 minute ago, IanR said:

 

But what you've done there is more typical, I'm assuming the recent poster has chosen this thread for the insulated raft, which does take the load bearing walls.

It was primarily to show how I'd dealt with the bifolds, but fair point.

[IanR]

1 minute ago, garrymartin said:

It was primarily to show how I'd dealt with the bifolds, but fair point.

 

But with a strip foundation and plinth wall there's an easy solution to the bi-fold, that and insulated raft doesn't have...

[garrymartin]

1 minute ago, IanR said:

 

But with a strip foundation and plinth wall there's an easy solution to the bi-fold, that and insulated raft doesn't have...

🤣 In my defence, you did say "insulated rafts/slabs" and I definitely have an insulated slab... 😉 

[IanR]

8 minutes ago, garrymartin said:

🤣 In my defence, you did say "insulated rafts/slabs" and I definitely have an insulated slab... 😉 

 

I did. To me it's and insulated raft, but that's not the subject name of the thread, although it is the content of the thread, there are also others on the forum that object to this type of insulated foundation and floor system being referred to as a "raft", so I was trying to not ruffle old feathers.

[FozzieKev]

On 01/03/2023 at 19:27, IanR said:

Here's my go at an over-engineered insulated raft, for a Garden Office.

 

As per @Iceverge, ground should be around 150mm below the finished floor level. No separation layer needed for EPS.

 

To do the chamfer detail on the upstand you'd need to make up a hot wire cutter. If not then a thinner upstand (25mm) will do. Upstand can be stuck and screwed to the base layer. You could, almost definitely, do it all in EPS100, rather the the EPS200 I've shown under the ring beam, as you won't be having a heavy roof finish on that 5° pitch.

 

 

 

So I was looking at this and thinking how would you go about putting bifolds in. My guess now would be to strip foot the front to the width of the bifolds, and use some engineering bricks/blocks for the bifolds to sit directly on tied back to the slab through the EPS.

Edited June 23 by FozzieKev

[FozzieKev]

On 19/06/2024 at 21:05, garrymartin said:

Looks very nice by the way.

[IanR]

On 23/06/2024 at 21:58, FozzieKev said:

So I was looking at this and thinking how would you go about putting bifolds in. 

 

There's a number of different options, depending on what you are trying to achieve. If you planned a heated floor (UFH) that would be used all winter then it's worth considering something more complex, but if you do not plan to heat the floor then a cold bridge along the bi-fold frame to floor is less of an issue.

 

The simplest option, to get a low threshold for the bi-folds would be to recess the raft to create a shelf for the bi-folds to sit in (cutting away the EPS upstand as required) and have a local step on the outside with a drainage path between the back of the step and the side of the raft.

 

To take this much further you'll need to share more info on plan for upper structure, planned surface outside the bi-folds, generic section of bi-fold frame and where the bi-folds drain to.

 

 

 

 

[FozzieKev]

Primarily office space, used all year round Mon-Fri 9am-6pm.

I have considered electric UFH, but I am also slightly put off from our days in a flat where we seemed to be heating everywhere else bar the rooms we were trying to heat… having said that it was built from a converted maltings and wasn’t necessarily insulated well.

 

Internal floor space, I am looking at 3m x3.6m, next to the boundary. Garden room will be full south facing on the shorter end which will have the Bi-Folds and I am considering triple glazing. The property to the east has a ground level 300mm lower than mine, and to the south is about 150mm.

 

I am looking at maintaining the door threshold consistent with the garage which is one brick above my ground level, and putting a trench and drain round to deal with any residual rain water. We live at the top of a hill, so don’t tend to have issues with flooding.

Frame to be 5” x 2” with a two 10mm flitch beams in to ensure spans at otherwise 400mm offsets. I think I can get away with a warm roof and am considering putting sedum on top of it.

 

For cladding I was looking at Cladco’s composite and using their composite battening, mainly because to ease in maintenance.