[tinyallotment]

Might have found a solution to the tanalised saw dust problem. our local saw mill will tanalise the timber after I have milled the angles and sanded the wood smooth so no more deadly dust.

It is going to end up costing about £35 + VAT per dome

Too late for this dome but future domes will be less toxic to build plus I can just add tanalising as a optional extra which the customer will pay for.

Paul

[pgkevet]

I've looked at building a dome a few times.. mostly cos they look cool. But a straight timber base on the ground with no easy way to install guttering, tanalised or not, would worry me. And in a greenhouse it's going to get watered inside as well (of course). Presumably chestnut or cedar would be the timbers of choice (or aluminium).

[tinyallotment]

I am in the process of designing a new base system that will solve a lot of the problems you mention.

I am thinking of building moulds to make cast concrete base sections that interlock and bolt together. The concrete base also incorporates a gutter leading to a sump with a float switch  to pump the water up to a barrel.

Paul

[pgkevet]

It might be possible to us ground anchors (down pipe sunk lengths with rebar or ally tube mortared inside) to raise the baseboards over a gravel trench. And if your dome follows the pic of the cmpleted one then it's also possible to run a channel over the doorway and round at the 'waist' height with a couple of gravity to waterbutt collection points... and then route a tap through the dome to have watering points from each?

I've been mulling over building a new bigger citrus house but that would need better insutalion than a single sheet of polytunnel plastic (for welsh winters). For me the simplicity of a multisided vertical construct with cupula type roof clad in twin-wall polycarb looks best...but stops it being a cheap build.

Has anyone tried sandwiching bubblewrap between two polytunnel plastics? Still condensation issues?

[HesterF]

My mum bought one of those (from kit) 30 years ago and it's still going strong. Seems to work well for her - she still grows lots in it! Just cleaning it is a nightmare.

[cloddopper]

A friend of mine , well an acquaintance more like,  has such a green house and it appears to be all worked wood joints , it's made  out of western red cedar , it must be a good 25 yrs or more old. western red cedar doe not need a preservative .

Once you makke a decent jig or three cutting repeatable joints is a breeze with a decent 1/2" router   & cut to length planed timbers.
 The rebated window panes are made from cut to size perspex that has been set in place & sealed with a long term flexible mastic which means that over the years they have gone opaque but still let the light in and it last much longer than poly greenhouse sheeting's.  The whole thing is set on cut to size outdoor concrete blocks that were set up  on a concrete foundation ,all are properly pointed as well. If I remember rightly there are also three windows that can be opened and kept open on a lockable window stay . Though now I have automatic venting stays on my big green house if I were to make another green house of any shape I'd be using the auto venting stuff .

    I gather that a welded metal jig was used  so that a petrol disc cutter  could quickly cut things to the right angle ..  The rules of trig & geometry needed for this exercise  say that the angles will be opposite and equal & congruent ) so it's just a case of turning one block over  to get the correct angles and infilling the difference with block work  cut at 90 degrees  . The bottom row of frames were set on a couple of beads of long life flexible mastic and also coach screwed and wall plugged to the block base.