Garden Room Office: Part 1 – Permitted Development Reg & Foundation Options

Part 1 in a series of how to build a Garden Room Home Office. In this episode, we cover the essentials of planning permission (aka permitted development) and how it shapes the design. Then, we dive into the design of the timber base frame and foundations and start refining the overall concept.

See full Playlist Here: https://www.youtube.com/playlist?list=PLF6PH1eEmrDm0gRSUfPjrHgeZotIhys5p

With two energetic young kids keeping the house lively, an outdoor workspace has become a necessity. After researching my options, it became clear that a self-build garden room is going to best suit our space, budget and need for quality. I may not be a professional builder, but months of research have given me the confidence to take this on!

Join the journey – In time I’ll be sharing detailed plans so you can build along with me. 🔨 Subscribe for updates & hit the 🔔 notification bell to follow the full build series!

► Website: https://makers-manual.com
► Patreon: https://www.patreon.com/makersmanual
► Instagram: https://www.instagram.com/makersmanual

► English Planning: https://www.planningportal.co.uk/permission/common-projects/outbuildings/planning-permission
► Scottish Planning: https://www.mygov.scot/build-shed-garage-greenhouse
► Span Tables: https://www.timberbeamcalculator.co.uk/en-gb/span-tables/
► Garden Room Guide https://www.gardenofficeguide.co.uk/
► Timber Merchant: https://tidd.ly/4mp11Af

CHAPTERS
————————————————-
0:00 Intro
1:14 Permitted Development
4:24 Foundations & Frame Design
10:29 Overall Design TBC

#planningpermission #diyprojects #gardenroom #homeoffice #permitteddevelopment

► Music https://share.epidemicsound.com/gavgsd

Disclaimer:
This description contains affiliate links, this means we’ll receive a small commission fee if you purchase a product after clicking a link. This is done at NO extra cost to you but you’ll be supporting the channel.

We’re going to build a garden room, as a home 
office and it’s going to look something like this. We wanted a room that was roughly 10m square. 
We thought this was a generous size for a two person office, without using up too much 
space in the garden. We found searching for a garden room supplier to be a minefield. Many 
structures were little more than glorified sheds, whereas the true garden room suppliers had 
somewhat misleading claims about quality and the initially advertised price was rarely the 
true price of a fitted structure. But after a lot of digging we found that for a similar 
size structure to what we were looking for it would cost somewhere between £8,000 and 
a whopping £25,000. After doing some quick sums we think we can build a high-end garden 
room for the lower end of that price range. So we’re going to jump in and we’re going to 
give it a go, we’re going to film the entire process and we’re going to let you know the 
materials we use the techniques we use, the mistakes we make along the way and the reasoning 
of why we’re doing it that way. And at the end of it all we’re going to put together a set of 
plans so if you like you can build along with us. Now I realize many of you want to get 
straight to the build and if that is you we have chaptered the video down below. 
But I think this bit’s really important, the design is initially going to be governed 
primarily by planning permission, or rather what we can design without planning permission 
(permitted development). When digging into the permitted development rules, the key takeaway 
for our purposes are that in England no part of the building can exceed 2.5 m if within 2 m of 
the boundary. If more than 2 m from the boundary, then you cannot exceed 2.5 m to the eaves. Now 
the eaves seem to be a somewhat subjective term, but in this context I believe that means to the 
bottom edge of the roof where it meets the outside wall. Here in Scotland the rules are a little 
easier to interpret. They state that the building can’t be more than 2.5 m tall, unless more 
than 1 m from the boundary. Then it can be 3 m tall to the eaves. There are of course other 
limitations but they’re more specific and not relevant to us at this point. Still it’s worth 
reading up on them, so if you are building an outside structure I’ll link the rules for both 
England and Scotland down below. The 2.5 m limit will become fundamental to this build. Basically 
every off-the-shelf garden room will be below the 2 .5 m limit and it pretty much defines what a 
garden room is. Anything above 2.5 m tends to need planning permission and it’s a whole different 
kettle of fish. Now 2 .5 m might seem reasonable, but it’s actually very restrictive. 
It’s hard to make a nice looking room, that’s well insulated and has enough ceiling 
height inside. We plan is to build a garden room in the corner of the garden and more than 
a meter from the boundary. That means here in Scotland we can legally make the buildings 3 
m tall to the eaves. But since we’d like to make this guide applicable to everyone we’re 
going to design around the 2 and 1/2 m limit, although we will keep our options open in the 
future to exceed this. Also if you’re building on a sloped surface, it’s worth saying that in England you measure from the high point of the slope. In Scotland you measure from the low point. At the end of this, 
the building will be classed the same as a shed or a greenhouse, so it doesn’t need to comply with 
any strict building standards. That being said, we want to build a quality structure so it 
makes a lot of sense to pay attention to these standards as they provide a lot of good 
guidance. The next step in the design process was deciding on the overall proportions of the 
room. We wanted to fit in two large desks while still having space to move around. On top of that 
we wanted to work with standard material sizes, so we could be as efficient as possible. In the 
UK we seem to be in an odd situation halfway between a metric world and an imperial one. This 
can complicate things when sourcing materials, for instance plywood tends to be sourced in 
imperial measurements. Whereas OSB tends to come in metric measurements. This can have 
implications throughout the build but on the whole it seems best to design around a metric 
standard. After much thought we decided to go for a floor size of 4.2 x 2.4 m. These dimensions make 
full use of the board lengths and require three and a half board widths. This option creates a 
stronger frame with fewer joints and less wastage. As for the rest of the design we’ve already 
planned that out but here’s a sneak peek… There are many different foundation options with 
no single best solution, however again the primary design limitation is the 2 1/2 m overall limit. 
This means we can’t use any foundation that raises the floor more than necessary. We also need 
to account for an air gap between the ground and the frame of at least 50 mm. This is to 
allow for air movement beneath the building which is essential to keep the building healthy. 
Ideally this distance would be more, but it simply isn’t possible with the height restriction. It’s 
now a good time to consider how the dimensions will stack up and show why every millimetre is 
important. But to do that we need to know what timber to use for the floor and ceiling joist and 
for that I look up a floor joist span table. These are tables that list how far a joist can span, for 
a given profile and joist centers. These tables can be found online and I’ll link this one down 
below. I know that we’ll be using C24 regularized timber, with 400 mm centers. I also know that my 
joists will need to span around 2.2 m with our frame design, and I want to find a timber with the 
least depth while achieving that span. In terms of dead loads, we can go for this column because 
we’re not going to have any permanent weight, such as walls resting across the span of those 
joists. It’s worth saying you get different grades of timber; C16 and C24 being the most pertinent 
to this conversation. C16 tends to be cheaper and more readily available, but with more defects 
is also a weaker timber. When I look at the C16 span table, these are the suitable joists. 
But they’re all deeper than I would like. When I look at the C24 span table these are the suitable 
timbers. I’m going to go for this one, because it’s strong enough and has the least depth. It’s 
worth noting that these dimensions are the finish dimensions you need for the timber, that is the 
dimensions you’d measure with a tape measure. Confusingly some timber yards like to list the 
nominal dimensions of the timber, or the rough cut size before it’s planned down to thickness. 
Now knowing the joist depth and assuming the same joist for floor and ceiling, we can look at how 
the dimensions stack up. 50 mm for an air gap, 120 mm joist, 18 mm OSB floor, 2100 ceiling 
height, and then assuming a cold roof setup we have 120 mm joist again, 18 mm OSB and 21 mm of 
roofing material. That equals a total of 2,447 mm. This is clearly a simplified example but you see 
why we need to be so careful with our dimensions. When considering the different foundation options 
I found this website to be a great resource. I’ll link it down below. Among my top choices were a 
concrete slab. This is a great option, especially on flat ground like ours. Floor joist can lay 
directly on the concrete and because it’s a solid platform the joist depth can be reduced. But 
concrete is expensive to lay at about £2,000 and if not perfectly flat then it can prove difficult. 
For us the cost was just too much. Another good option is Plinth foundations these are pre-formed 
concrete feet that the frame sits on. If sunken into the ground they can keep the frame (lowish), 
and provide a solid foundation. They are however expensive at around £1,000. I’ve also seen this 
done in a more DIY fashion using breeze blocks, but levelling these sufficiently can be extremely 
challenging. Ground Screws are a fashionable choice and for good reason. They can support a 
lot of weight and are relatively easy for DIY installation. Getting an even height is as easy 
as screwing them a little deeper and they can sit low to the ground. They’re also a great choice for 
sloped ground. At roughly £500 for a DIY install, they are the cheapest option so far and an option 
we were tempted by. The option we chose however, is not often considered and I’m not sure why. When 
we put our shed up it was on very uneven ground so we supported it via wooden fence post set into 
Concrete Piles. This is easy to install and it was very cost effective. The only reason I can think 
it’s not popular is because the wood can rot over time, but exchange that wooden fence post for a 
recycled plastic post and all concerns of rot have gone. We consulted a professional about this and 
they confirmed to us that it’s a viable and good option. All in all, it’s the cheapest option at 
around £350 and it should be the easiest method to install. After a great deal of thought this 
is the design I came up with for the foundations and timber frame. I wanted to maximize material 
efficiency while looking for an easy build and a solid structure. With 15 posts total, this equates 
to roughly a post every meter. I contemplated 12 posts, as with some reckoning that’s still plenty. 
But with advice generally to go between 12 and 15, I chose the cautious approach and went for 15. 
Unfortunately for my compulsive need of symmetry this meant the post couldn’t be equi-spaced, 
unless I chose a frame design more like this. Some like this design because it reduces the 
potential of bounce in the floor and transfers the forces better. While this is good advice, I 
felt the benefits would be very little in this situation. This is a much smaller structure 
than a house ,the loads on the floor will be relatively low and the majority of those 
loads will be around the perimeter. Also with three posts in the center, I cannot foresee any 
bounce. There would also be stages of the build where this design would be much more troublesome, 
installing the joist hangers in this small gap for instance. With this design I’m able to be more 
material efficient and have a simpler layout for the insulation and flooring. All the insulation 
and noggin can be cut to the exact same width, except for the outer pieces. This should allow 
me to batch cut the insulation and will be both quicker and more accurate. Also with this 
design I can go for a flooring pattern like this. With fewer joints, the structure will be 
stronger and again it will be an easier build. And lastly there are double joists on the outside 
to increase the strength and distribute the load. It also provides a more substantial platform 
to screw down into later in the build. As for the rest of the design, it’s going to look 
something like this. But, I don’t want to get into the details right now, because well… 
we’ve changed our minds. Although this design was based on another design that we liked, we realized 
that it’s not going to be practical as an office, so we’d like to tweak the location and size of 
the windows. Also we realized that we can make the building bigger and with more insulated for free. 
Our thought process and how we can achieve this it gets a little complex, so rather than getting 
into it now I thought for clarity it’s better that we tackle that when we put up the walls 
and the roof. And that’s the design complete, as far as I have it. In the next video I’ll 
dig the foundations and simultaneously build the frame. I’m a little further ahead with 
the build than I am in my video releases, so as soon as I have enough built that I’m 
confident in the design I’ll release plans so you can build this with me. Those along with key links 
I’ve mentioned in the video, will all be linked below. So stay tuned, there’s lots more to come 
from this series and until next time… cheerio.