Conservatory Design & Build - Part 1 - Enabling Works

We'd previously thought about erecting a conservatory, but the difficulties to be overcome at our location seemed too complex to address without a lot of time to spare.

But we're currently spending much more time at home - I'm not sure if our usual autumn holiday will even be possible this year - and of course we also haven't been spending money on travelling, so now seems as good a time as any to look at a conservatory.

We began exploring options a month or so ago.  A DIY conservatory kit was first considered, but the companies I approached were not very responsive to non-standard layout queries and technical requirements.  So I very soon lost patience with them.

Design and Project Management is actually my business, so I decided that by designing and sourcing everything myself, we would get exactly what we wanted and it would likely be much less costly too, without a middleman taking a cut.

Anyway, finalising the required layout and design was the first objective.  We looked at several possibilities from a double-ended lean-to layout of just 3.5 metres length, then a similar arrangement at 5.0 metres, before finally electing to bring the new building right up against the face of the existing extension, making it single-ended and 7.4 metres long in total.   There are a few challenges in connecting the buildings together, as will be seen in the photo diary commencing below.

For the basic conservatory layout, we considered either dwarf walls or full height glass all around, but in the end I designed a hybrid version with a dwarf wall on the northern aspect that's visible to passers-by, and using full height glass for the long western elevation which can't be seen from anyone outside the garden, so privacy is not an issue here.

basic drawing of the design ...

We looked into the planning requirements and concluded that this design met all the criteria to be considered 'permitted development', e.g. additional side width not greater than half the width of the original house, nothing protruding forward of the principal elevation fronting the road, single-storey conservatory with total height < 4 metres, total built area less than 50% of the total curtilage, etc.

Unlike house extensions for which planning permission is required, conservatories are a special case and are exempt from having to use materials of a similar type, style and colour as the original house, although we'll try to make the front elevation blend in as sympathetically as possibe.  Additionally, Building Regulations are not applicable to conservatories provided a few very simple rules are followed.

But if you're looking to build something similar, then you'll need to do your own research on planning requirements and regulations depending on the design, location and size of the conservatory.


One feature of the new conservatory is that it will cover a large area of unsightly and damaged concrete.   I've previously prepared plans to dig-up all the driveway & hardstanding areas to the side and front of the house, and replace them with a combination of new concrete and block paving, but at >80 square metres in total this would have been a huge project in itself.   By building the conservatory in the chosen location, it will reduce the required future driveway works by 20 square metres.

With our basic conservatory design finalised, a few initial survey measurements were made to confirm the sizes, the drawings were checked and then the main materials were ordered.

On the northern elevation, the front of the house, there are two identical window units and a half-panel uPVC door.   The conservatory will effectively cut off direct access to our existing front door, which is actually located on the side of the house, so we needed something at the front of the conservatory with a letterbox etc.

For the long length of the western elevation, there are four identical full-height window units and a framed pair of French doors.   

All doors and windows were ordered from the one supplier, so the framing design and trim details are all in the same matching style. 

Including corner posts, cills, frame interconnectors and a few other accessories this supply came to around £3,200 in total.   This seems reasonable for around 10 metres length of glazed doors and windows, all A+ rated double-glazed and using toughened glass throughout.

For the roof, I ordered all the individual components for a self-supporting lean-to roof system, from a specialist roofing supplier.   These roofs are used on carports and many other open & closed buildings in addition to conservatories.   

Basically, there are eaves beams which sit atop the glazed units, ridge beams fixed to the house wall, reinforced glazing bars that span between these beams, and glazing panels.   This particular roof system is strong enough to support a full glass roof, but we opted for 35 mm thick multi-wall polycarbonate panels which are lighter and cheaper than glass.    We ordered the glazing panels to be cut to the exact sizes required from my drawings, but everything else was procured in standard lengths and will need to be cut to size on site during the build.  Around £1,500 all-in for the roof components.

The windows and doors are all made-to-measure and are therefore the long-lead items on the project, at around nine weeks from order, and we're still awaiting their delivery.   In contrast, the off-the-shelf roof components were all received in just a couple of days after ordering.

So with the major procurement activities in hand, it was time to look at the Enabling Works, in our case to first construct all the required plinths, walls and flooring etc to allow the proprietary items to be erected immediately after delivery.

With a long delivery period for the doors & windows, we seem to have plenty of time in hand to complete these works, but there are a lot of individual tasks to be considered.

What follows is Part 1 of a photo diary of the conservatory preparation and build :-

before starting - unfortunately, that beautiful climbing hydrangea 

had to go.  It's now been pruned, dug up and is living in a large pot

demolishing the reinforced concrete door canopy

canopy roof section cut into 16 pieces for safe removal -

 it's 70 mm thick & steel reinforced

after removal and dressing.  I think this remaining canopy section also doubles as 

the lintel over the front door.  It must have needed a crane or hoist when it was 

originally installed.  The top length will be covered by the roofing ridge beam.

partially building the conservatory suspended floor, working away from 

the highest local grade level near the centre of the office door frame, to 

establish the required elevation of the top of the foundation ring beam

shuttering for the ring beam & and rebar for the dwarf walls, 

after locally pressure-washing the existing concrete slabs

includes a 150 mm deep foundation trench dug 

between the existing concrete slabs

existing concrete slab drilled, and rebar 'keys' 

fitted every 500 mm within the ring beam shuttering

first concrete cast, the ring beam (03-Aug-20)

due to the slopes, the ring beam casting varies from 

<60 mm thick at the far end to >150 mm at this front edge

at the thin end of the ring beam - the formwork was unscrewed for an 

initial inspection (04-Aug-20), and then the outer shuttering was put 

back loosely for protection during full curing of the concrete (around 28 days)

shuttering prepared for the front dwarf walls, from 

18 mm thick OSB (this will also be used for the flooring)

I wasn't sure whether to try to cast this 100x30 mm ligament at the end of the outer wall, 

or simply to fix a piece of timber or steel in place afterwards (to hide the window corner 

post from the front view), but if it doesn't cast properly it can always be repaired later

wall casting (05-Aug-20) - top straps added to prevent bowing-out 

at the top under the 600mm head of liquid concrete

total concrete for ring beam & walls was from 100 kg cement, 

550 kg ballast plus around 60 litres of water to mix

formwork removed from the walls (08-Aug-20)

the top of the wall will need dressing before the windows & doors arrive

the formwork has shifted slightly during casting - this inside corner 

of the ligament is no longer square and will need grinding back 

by 10 mm on the inside face after the concrete has cured for a few 

weeks - the corner post for the glazing must fit into here

the new garden tap location, now moved outside the conservatory area

with the tap relocated, the first two floorboards can be fitted.  They're coated with 

a floor paint - although the OSB is supposedly 'moisture resistant', it could be damaged 

by heavy rains while we're waiting for the glass and doors, not expected until mid September

it butts up very well against the office door frame -  it proves everything is built square !   

We need to cut and paint infill pieces for the gaps near the side walls - the boards 

are standard 8'x4' and not quite long enough for the full width of the conservatory

flooring edge at the concrete ring beam - the boards sit around 12 mm 
below the top face of this beam, onto which the full-height glazing will sit

End of Part 1.  

To be continued ...