Building a room in a small garden

Building a room in a small garden

We needed an extra room that could be an office, a telly space for teens and even a spare bedroom. The garden was the obvious place but it is a pocket handkerchief space. Joiner and builder Tim Mansfield wasn't fazed.

Abby Trow. Photographs by Mike Trow
garden rooms are fab

Our north London garden measures 27ft x 19ft.  Our garden room measures 11ft x 8ft 6in. Built over seven weeks by the bare hands of the brilliant Tim Mansfield, it has an eco friendly green roof and is made from wood with full width bi-folding doors - and it has sheep's wool insulation and cedar cladding. It's a fantastic room that cost £16,350. The Meadowmat for the roof plus the clay ball substrate and delivery cost an additional £750. A m2 of Meadowmat, by the way, is very heavy.

It's nearly a year since Tim started building the garden room and it's now hard to imagine life without it. The shed, as we call it, has wifi-enhanced 'tiny house' appeal, which means we all want to retreat to it - me to read, write or listen to the radio, our teenagers Hari and Noah to take their Xbox down there and play video games, while their dad Ajay works in it two days a week, does his guitar practise in there (thank god for double glazing) watches Columbo on Sunday afternoons - yes, there is an old telly in there.

Check whether you need planning permission

People were sceptical as to whether a garden as small as ours could accommodate a room of a meaningful size, but our friend Tim, a joiner and builder, thought it would be a fun project for him so he drew up some plans, submitted them to Islington Council and nine weeks later we were granted planning permission - and the planning officer we spoke to said a green roof would definitely increase the likelihood of planning permission being granted. (In case you think you don't need permission to build a small structure in your garden, you don't if you own a whole house, but we have the upper flat in our building, so we did need it.)

The interior walls are painted with Dulux's Heartwood in a 2 parts Heartwood to one part white mix
The shed looks very neatly positioned... Tim the builder is a master of precision
Day one - digging out the space, digging down a food for the concrete foundations
The timber frame going up and the floor joists are laid on the concrete
The frame starts to be covered. The ceiling height we have now the room is complete is just under 7ft
The exterior comes on - Tim has to put layers of a fibreglass material to make the roof watertight and green roof suitable
We used Thermafleece sheep's wool insulation. The shed is very warm!
Plasterboards is on and Tim does a skim coat of plaster
Once the plaster dried, Tim painted the walls in Dulux's Heartwood - a ratio of 2 white to one Heartwood.

You can, of course, buy a room from a garden room company which will be built off-site and take a few days to install. We looked at these options but they came in at well over £20,000 including the bi-folding doors and a hardwood floor. Tim estimated it would take him 6-8 weeks to build a simple rectangular shaped room himself, hiring in some labourers when heavy quantities of materials needed to be shifted. Indeed one problem with our flat is access - you have to walk up a flight of stairs to get into our flat and then walk down the fire escape stairs to the garden, so bringing in materials did make the job extra arduous. Tim is a man of herculean strength it must be noted.

The process

TIm explains that you have to dig out the space for the building and dig down about 1ft for the foundations. Before pouring in the concrete, he laid a sheet of heavy plastic that acts as a damp proof course and it goes partially up the side walls. Tim then made the timber frame for walls and roof and cut a space for a 1m skylight. Sheets of marine ply were attached to the frame, while on the inside, sheep's wool insulation, Thermafleece, was laid in between the joists. The internal walls were then clad with pink (waterproof) plasterboard, plastered and painted. However, the space between the floor joists was insulated with Celotex - less eco friendly but Tim felt it was more solid and suited to a floor. 

The green roof wasn't so easy for Tim as he'd not done one before. He went on a three-day course and then got down to it. So the marine ply is laid on the frame, which has been made a slight angle to allow for drainage. Tim then had to build up layers of a fibreglass coating to ensure water tightness. This process happened over the best part of two weeks. 

In between times Tim laid the armoured electricity cable from our house down to the garden - he tacked it to the side of our fire escape staircase. He also had to put in the wiring for the lights, the wifi and sockets and two wall mounted electric radiators (we have found that in fact one radiator would have been sufficient). The exterior wall which you can see from the side angle he clad with cedar planks, which he coated with three layers of an Osmo oil so the lovely browny colours are maintained and it doesn't fade to that silver grey. The cladding boards on the back of the shed, which you can't really see, is a cheaper pine, which saved us money. 

The green roof materials were quite a problem because of the weight of the rolls of Meadowmat. We wanted a wild flower roof garden, and Meadowmat was the product we chose. It's delivered in 1m rolls, and is ready seeded and looks green and bouncy. But before you get to unfurl it you have to cover the roof with a membrane, a thin layer of soil then a thick layer of a clay ball subtrate. This substrate is lighter in weight than soil and it allows for easy drainage. The rolls of Meadowmat were then hoisted by Tim onto the roof and unrolled. And voila, a jolly green roof. About two days work from when the materials were delivered.


Tim put a shelf along the entire back wall, painted in the Heartwood emulsion to match the walls. The skirting boards are likewise the same colour as the walls
Tim in the garden room with the bi-fold doors fully opened.. we sure do need some beautiful plants to look at...
Getting the layers of green roof on - the product we used is Meadowmat
Tim put in a skylight for more natural light

Interior decoration

The fun part. Except not being a vast space there wasn't the need to buy sofas and coffee tables. We chose an engineered oak floor, which cost just under £400, which Tim bought from his timber merchant PO Joyce in East Finchley. The walls were painted a soft pinky heather colour using two parts white paint to one part Dulux Heartwood paint. The colour is quite dark, so we experimented with various ratios of white until we got the shade we liked. And I wanted some storage so Tim put in a sturdy shelf that runs the width of the room. It's quite deep so holds a lot of books, pictures etc. It was a great idea and works really well. 

We knew we'd need curtains because of the span of glass bifolding doors. And Tim realised the curtain rail had to go round to the sides of the walls, so you could push the curtains out of the way when the doors were open. The best option was to have a  Swish plastic rail which bends around corners, which Tim fitted. And I was thrilled to find a pair of pink velvet curtains, lined with blackout fabric, on Ebay for just £20. They fit the room perfectly and give total privacy when drawn. Unfortunately they are a bit too heavy for the rail so we will have some lighter curtains made at some point. But with full width glass doors you do need curtains.

Lighting is provided by two wall mounted Anglepoise brushed steel downlights, one on each wall. They cost £75 each and we bought them at Heal's. Other than that we bought down from the loft an old silk rug for the floor which I'd bought in India years ago, a Fat Boy beanbag, a writing desk and a wooden chair, plus a red foam cube by Quinze & Milan, which again, I'd bought years ago. We also bought the Kilo white metal and oak two-tier unit from Habitat for the television to sit on. This piece costs £130. 

In short, we wanted an eco friendly garden room made from wood, which is large enough to want to spend time in and, of course, to work in. Tim did a brilliant job, it's a lovely room, and we can't thank him enough. 

Tim says: 'It was a really good project, albeit an exhausting one. I'm delighted with the finished result, it's a simple, timeless design and it's constructed in a way that should see it give decades of service - I hope.'


Timber, concrete, Thermafleece, cedar planks, coping stones for the roof edges, Meadowmat green roof, engineered oak, Dulux Heartwood paint

If you would like to contact Tim Mansfield about small building projects, please email and we will forward your messages to him.