Pergolas - Phases 2 & 3 Works (the Summerhouse)

Following on from my post in September about building the pergolas, for a while afterwards I was thinking that the larger one to the side of the house seemed a little lost and disconnected with the rest of the garden.   

Not wanting to sound like a pretentious tosser, but what it needed was anchoring within the landscape.

So Phase 2 was implemented, which involved connecting this pergola with the one at the side of the house extension by extending the outer beams of both structures until they met each other.  This also meant reducing the height of the semi-goliath pergola slightly so that the extended beams were both at the same elevation.

The longest extension beam needed another vertical post to support it, but by this time I already had the summerhouse in mind (the Phase 3 works) so this new post was positioned where it would also form one of the new building corners.


I designed the summerhouse to be an open structure, using more trellis panels of the same style as the pergolas, and with a canopy over for protection from sun and rain.  It's located on the area of artificial grass I laid in 2015 which we termed the winter garden because it's where we had several containers of evergreen plants - there are also existing garden seats and a table which will now sit within the summerhouse footprint. 

There's a route provide through the summerhouse onto the side lawn so we don't always have to walk around and through the pergolas.

Not much to say about the basic construction which again was straightforward timber works, but the roof and canopy design is interesting.  

The lateral beams that form the upper part of the summerhouse are all at the same elevation as the pergolas, and I didn't want anything sticking out higher than this level to ruin the lines of the whole combined structure.  

So under the roof beams, I formed a shallow apex from three 3.5 m lengths of galvanised steel handrailing tube, which span the full length and are only connected at the sides of the new structure.

the three canopy support tubes ...

The central tube at the top of the apex was drilled and tapped along its underside, and fitted with 9 pairs of rope cleats which are used to secure a tarpaulin cover.  

pairs of cleats attached to the underside of the apex tube ...

Two aspects of this canopy design are of note :-

• by wrapping the tarpaulin edges 180 degrees around the tube, the rope tension supports a higher tension in the top stretched section of the tarpaulin (google 'belt drives' or similar for the maths if you're remotely interested ...)   So when the wind tends to lift the canopy and induce additional membrane forces, the full effects are not transferred to the securing eyelets which is where tarpaulins are most prone to failure.

• by terminating the edges of the tarpaulin inside the canopy and at a higher elevation than the supporting tubes at the eaves, it creates a drip-point on the tarpaulin at the underside of the eaves - the water cannot travel further around under gravity and so must be shed at this low point, keeping more of the area under the canopy dry.

We bought a medium-duty tarpaulin from 260 gsm material - it was actually advertised as heavy-duty, but the widespread misuse of such descriptive terms in marketing is a subject for a blog post in itself ...

The tarpaulin was supplied with 4 lashing eyelets along each side, but I added another three eyelets between to provide 7 rope attachment points on each of the two edges to be secured.

inside - that's the largest of this year's pumpkins on the table ...

The canopy's been up for several weeks now and has already encountered 40 mph westerly winds with no ill effects, but we'll reserve judgement until (and if) it survives the whole winter.  

I'm prepared to sacrifice this particular tarpaulin - if it doesn't last, we've the options of either only fitting the canopy for the summer (although we often get high winds then too, so this isn't a preferred solution) or using a truly heavy-duty cover made from thick canvas or sailcloth.  Or as a last resort, fix rafters from angle irons or similar between the steel tubes and make a boarded roof with felt or shingles on top.

Finishing touches included constructing box planters at the two corners of the summerhouse nearest the house.  These cover the cut-outs I had to make in the artificial grass to dig the post holes.   We've already planted very young climbers in these boxes - a Winter Jasmine (jasminum nudiflorum) at each corner and a single evergreen Star Jasmine (trachelospermum jasminoides) in the centre near the summerhouse front entrance.

Along the sides, to bridge the gaps between the trellis panels and the corner posts, we fixed galvanised steel eyehooks and used a length of tri-colour polyprop rope wound into a diagonal pattern.  I'd seen something similar on one of the gardening programmes on television - it's simple, but I think quite effective.

There's also a potential Phase 4 of the works to consider, which is to construct a floor inside the summerhouse from decking boards.  My wife prefers this idea as it makes the space more of a complete building, but I quite like the artificial grass ...