Maximising Useable Height in Block & Brick Garden Room

[Kalibre46]

Hi,

I'm hoping to embark on a rather large (50sqm) garden room project. I'm looking to do this under permitted development so I will be limited to a total height of 2.5m above ground level. It will of course require building regs approval because of electrical work, boiler etc.

I was hoping someone might be able to suggest the best foundation/slab/floor/roof construction to meet this criteria:

1) It's very close to some big trees, so I'm erring towards a helical pile system to minimise disturbance.
2) I understand brick and block will be heavy, but I'm looking to build up to my boundary on three sides, so I'm thinking that I can't use timber construction because I have no access at the sides to apply render etc. Any ideas?
3) In an ideal world (but might be asking too much) I'd like some sort of green/sedum roof so it'll look in keeping with the garden when viewed from above.
4) I'm concerned that with a total 2.5m height limit that I might end up with an unworkable interior ceiling height once the slab etc is added. I don't know how I could go about getting the interior floor level as low as possible without breaking any rules....

I'm not a builder so excuse my ignorance, but can anyone suggest the best combination of foundation, flooring and ceiling construction so that I can achieve everything I want but stay under the height limit?

Many thanks in advance,

Doug

 

[John D v2.0]

have you thought about getting full PP for it? If you're putting a garden office up then it'd be a big hassle, but for something of this scale, you may find it worth relaxing some of the restrictions (unless you believe it will be rejected)

 

[Kalibre46]

Thanks John. Yes I have done, it is for a garden office/gym. However given the placement of the building and the proximity to neighbours I wouldn't really want it higher than 2.5m anyway, so it's kind of a mutual limitation if that makes sense. I would be worried that if rejected as well for any reason that it might hamper our chances of getting it done under PD anyway, as I've heard that happen before.

 

[Notch7]

Ive built projects in timber stud construction and clad the outside in render board. I did a job where the client wanted a conservatory tight to a garden wall, but didnt want to lose as much as a cavity wall. Also we couldnt dig a foundation next to the wall as it have undermined it, so we built concrete pads, steel beams and encased in concrete,

Ive used 6 x 2 or 4 x2, 18mm osb, tyvek housewrap, 50 x 25 tile batten, render board.

Timber construction is far more forgiving of foundation movement than masonry construction.

 

[Notch7]

Regarding height, Im building a gardrn office about 5m x 4m and under 2.5m Ceiling height is going to be 2150mm, but thats with bottom of floor joists 100mm below adjacent ground level, and a 350mm thick roof including a small upstabd and flat glass lantern.

You will really struggle building a bigger footprint and under 2.5 high. You will need to dig down!

 

[Footsoldier888]

By going lower in the ground you won't be breaking rules but laws - of nature! In other words it gets expensive because you have to waterproof everything.

I'm thinking this sounds like a job for a steel frame construction of posts and beams. You could possibly have a few pent roofs going from low to high, or just a bunch of roofs at different angles. It would relieve the flatness of a large internal space.

On the infill panels you could have wood cladding to blend in with any fencing or cement particle board for a rendered appearance.

Regarding green roofs you need some beefy joists which might reduce the height, unless you went for more steel.

It's worth looking at agricultural buildings as a starting point.

 

[Kalibre46]

Thanks all. Some food for though there.

One other question, is there any limitation on how close we can build (under PD) this structure to the boundary? Anything in regs for minimum access etc?

Cheers.

 

[John D v2.0]

Thanks all. Some food for though there.

One other question, is there any limitation on how close we can build (under PD) this structure to the boundary? Anything in regs for minimum access etc?

Cheers.

No you could even build a party wall if you have the right notice to next door.
However if less than 1m you have to make sure the wall is mostly non combustible. You can have max 1m2 of window of that sidde.
If you're using block work it would be fine but if you use timber you'd need effectively triple boarding on both sides
This is to stop a great fire of London style spread of fire between properties.

 

[Footsoldier888]

I think the issues are primarily about things like not discharging water onto your neighbours property, which is a no no, ease of maintanence and foundations undermining walls or fence posts. Basically you don't want to be making a rod for your own back and end up getting into some horribly expensive neighbour dispute by building right up to the boundary. 30cm inside ought to be fine if you don't have foundations deeper than your neighbours wall foundations say.

About your structure - another idea I had was to go down a different route to the steel post and beam grid idea and that is to build a series of connected smaller buildings. You could even think about leaving some garden in the middle, you would get a lot more natural light this way.

Another but more wacky one is to consider a hyperbolic paraboloid roof! Hardly likely I know but at least it gives you an idea of what can be achieved if you are prepared to think outside the box.

Obviously check the rules though, not sure if the 2.5 restriction applies to the whole roof or just the boundary facing section.

 

[Kalibre46]

No you could even build a party wall if you have the right notice to next door.
However if less than 1m you have to make sure the wall is mostly non combustible. You can have max 1m2 of window of that sidde.
If you're using block work it would be fine but if you use timber you'd need effectively triple boarding on both sides
This is to stop a great fire of London style spread of fire between properties.

Thanks, very interesting. I would be at the boundary on three sides (all just fences, no neighbouring buildings). The only windows would be on the fourth side facing back down the garden towards the house.

 

[Notch7]

In England yes, in Scotland no.....I think.

England 2.5m high if building within 2 metres

 

[Kalibre46]

I think the issues are primarily about things like not discharging water onto your neighbours property, which is a no no, ease of maintanence and foundations undermining walls or fence posts. Basically you don't want to be making a rod for your own back and end up getting into some horribly expensive neighbour dispute by building right up to the boundary. 30cm inside ought to be fine if you don't have foundations deeper than your neighbours wall foundations say.

About your structure - another idea I had was to go down a different route to the steel post and beam grid idea and that is to build a series of connected smaller buildings. You could even think about leaving some garden in the middle, you would get a lot more natural light this way.

Another but more wacky one is to consider a hyperbolic paraboloid roof! Hardly likely I know but at least it gives you an idea of what can be achieved if you are prepared to think outside the box.

Obviously check the rules though, not sure if the 2.5 restriction applies to the whole roof or just the boundary facing section.

Thanks for the info. The idea of smaller buildings is one that I had considered actually, mainly because there is a slight gradient across the garden, nothing major but enough to make the 2.5m max heigh a challenge end to end without digging down at one of them! Smaller buildings could mitigate that risk and make the design more interesting for sure.

I do love those hyperbolic roofs, but alas the 2.5m restriction would make that very difficult. The wording on the portal suggests it is measure from the highest point on the structure.

 

[John D v2.0]

Another but more wacky one is to consider a hyperbolic paraboloid roof!

is that this one?

mainly because there is a slight gradient across the garden, nothing major but enough to make the 2.5m max heigh a challenge end to end without digging down at one of them! Smaller buildings could mitigate that risk and make the design more interesting for sure.

The 2.5m is from the highest natural ground level around the building, so a slope works in your favour.

 

[motorbiking]

When i built mine, I used a kind of home made SIPS system that i made and pre treated befor assembly. Then all i needed to do was mastic the joints and screw edge batten over them, as the panels were secured from inside. It was a tight squeeze but worked. The problem you have however is size. anything over 15m2 has to conform to the non-combustible rule.

 

[Kalibre46]

is that this one?
View attachment 140285

The 2.5m is from the highest natural ground level around the building, so a slope works in your favour.

I've heard this, but wasn't sure if this was an official written or unwritten rule, or simply down to the individual building control officer being prgamatic. Any ideas? I'd hate to commit to a design building this advantage in only to find they say no.