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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    My garden has a 10 degree slope, facing south. I'm planning to build a greenhouse with a masonry wall partially dug into the ground on the north side, and to use a salvaged aluminium greenhouse for the glazing on the south side. The greenhouse will be 7.5m long (across the width of the garden) and 4m wide.

    I've already built a smaller one in the garden, and it works nicely, with raised beds on the north side which give some structural support to the part of the wall that acts as a retaining wall.

    For the second greenhouse, I'd like the north wall to be the maximum height I'm allowed, 2.5m, and have a single pitched roof of about 20 degrees.

    My question is about how to build this north wall. It must need some structural design - building a single layer block wall seems precarious, as I don't want to rely on the roof structure to brace it. There'll be masonry returns at the ends - the north ends of the east and west walls can be masonry for a metre or more (the rest glass).

    Lay the blocks flat so making the wall 220mm wide? Would that be sufficient? Maybe there's some more appropriate building material/method?

    I've attached a sketch. Note, there a bit of a slope E-W too.

    The ground levels are pretty accurate I believe. In the sketch, I've cut a level path down the length of the greenhouse. It's about 600mm deep at the west end.

    On the south side a block wall under the glazed area seems straight forward. The salvaged greenhouse sides are 1.3m high, so a low block wall is needed underneath to give the required height.

    The north wall, sketched in with blocks looks scarily dodgy. But it shows the scale and shape of things anyway.

    The roof, I'm assuming corrugated PVC. Can't afford glass. The support for the roof will have to be timber, rafters to the top of the north wall, and some timber support on the south end of things, independent of the block/glazed south wall.

    The west wall, I imagine to be masonry at the north end, to help support the north wall, and bits of salvaged greenhouse on the south end. Something similar for the east wall, except I'll put a door in the middle.

    Thanks for any suggestions,

    • CommentTimeFeb 1st 2021
    You don't show the returns at the ends of the wall in your sketch? But they will be there? I'd add a buttress or two along the length of the wall to help support it. You could consider insulating the north face of it too, so it will act more effectively as a solar heat store.
    Have you considered building the base wall in blockwork to the height of the front dwarf wall, and then having the rest of the greenhouse built using studwork? While having the the rear wall of the greenhouse in blockwork would give you thermal mass, it wouldn't be great for insulation. With studwork you can insulate between and behind the stud, and the whole structure would be locked together with no worries about how to support the high blockwork wall at the rear. Thermal mass can then be added with water filled barrels at the back of the greenhouse.

    I'd considering building one of these solar greenhouses, so if you could start a discussion thread with your progress, that'd be brilliant.

    I've been looking at the solar greenhouse here for inspiration:
    Sorry, I didn't add the returns to the sketch. How much of a buttress do you reckon?

    I'm also considering using blocks to build up above ground level then using timber frame above that. Timber would be less of a heat store than masonry, but I have a stream nearby which comes out of a long tunnel at the end of the garden. So the water is 12 degrees pretty much, all year round. I might pump that through some radiators in the greenhouse in winter. I expect that would be all the heat increase I'd need, enough to guarantee it being frost free anyway.
    Hi Pile-o-stone,

    Sorry, missed your reply. I'm currently drawing the half timber option you suggested as it happens.

    The greenhouse you linked to looks impressive, but I need to do something custom on account of the slopes in the garden. Also, the glazing I'm using a 3.8 metre long greenhouse I got from freecycle. I can use both sides joined together to make a 7.5 metre long greenhouse.
    Here are a couple of snaps of the first greenhouse I did. It looks pretty awful inside right now. Because of bird flu, I had to move my hens into the greenhouse for a while. the rats followed them. Now the hens are gone, and the rats almost gone. But you can see the raised beds on the right hand side, which help support the block wall behind it. The photo taken from outside (not great, sorry! Restricted access) shows the front of the greenhouse made from two sides of an old aluminium greenhouse built onto a blockwork stud.
    • CommentTimeFeb 1st 2021 edited
    I don't know much about the subject of walling. I don't even know at what point a wall is affected by buiding regs or needs a structural engineer's approval!

    I did find https://warwick.ac.uk/fac/sci/eng/elith/publications/all_publications/elith-w03.pdf which has quite a lot of explanation and mentions such possibilities as 'crenellated walls'. But I suspect a timber frame might be better.

    I've long liked the possibility of soap bubble insulated greenhouses as well (see http://www.solarbubblebuild.com/ ).
    • CommentAuthorEd Davies
    • CommentTimeFeb 1st 2021
    I'm not sure if this is on-topic or not but it's a story which is at least mildly amusing: a neighbour had her handyman/gardener build a retaining wall across her steeply sloping garden to divide it into two much more level bits. I had a chat with him while he was backfilling above it and asked what bracing it had. He said none was needed and dismissed my sceptical looks in a “what do you know, office boy” sort of way. Sitting at my desk later I was doing calculations on the bending moment at the bottom of the wall when I heard a load crump sound. Fortunately no people or pets were involved.

    I doubt a structural engineer's input would be expensive and it'd give you, and perhaps your insurers, quite a lot of peace of mind.
    Hi Ed,

    Between Covid and Brexit, every one of my several small income streams have come to a dead stop. I am not eligible for furlough money nor any benefits. I'm 64, and soon to be living on a pension of £100/week. I figured I'd invest a part of my savings in some degree of food self-sufficiency. It's not what I planned for, but probably the best I can do. There'll be no structural engineer coming round.
    John, following on from your comments above about time rich, cash poor, what can you get hold of that won't cost you much/anything - build with that.

    Sloping site, what about digging into the ground level a bit, and doing a rammed earth rear wall below ground, using old car tyres. Garages I think pay £1 per tyre to dispose of. Say you dug in 1 metre depth, plus a bit more below the internal floor level for a bit of a foundation. That only leaves you a metre above ground at the rear. Timber and salvaged EPS or what ever to pack and line the stud. Set vertical steels into the tyres as you build to act as restraint straps for the timber frame, to counteract up lift.

    You presumably aren't too worried about a bit of damp coming around the car tyre wall (french drain behind to help), which is the tricky part about building below ground. If you were very clever, you might take the tyres above ground, and find something to cover up the unsightly look. Could even put some earth on the outside, sloped to reduce the load at the top, and grass seed it. Just compact the floor, with maybe gravel over the top. Make some duck boards to go over the gravel to make it posh.

    Low cost, low tech, re-use as-dug materials, thermal mass, bit of self-watering at the tyre wall. You could even do raised beds using the tyres, which would give a bit of extra retaining wall strength at the rear.

    Probably all a load of nonsense, but might have sown a seed for other ideas???
    Posted By: John Pedersen I'm 64, and soon to be living on a pension of £100/week. I figured I'd invest a part of my savings in some degree of food self-sufficiency. It's not what I planned for, but probably the best I can do.

    I was thinking the same thing for my retirement, having a degree of self sufficiency to help make my pensions go further and to provide a bit of security against economic downturns and other global or countrywide disruptions. COVID has made this even more firmly rooted in my mind as the way to go.

    My plan is to build a highly insulated and highly air tight eco house with private drainage, rainwater recycling and perhaps a borehole for drinking water (or spring depending on how lucky I am with my land purchase). I'd have large roof mounted and ground mounted solar arrays, batteries for storage and a ground source heat pump. In the garden I'd plan on having a large part of the land given over to an allotment that was based around a large all-season greenhouse. This would provide me with a hobby for retirement and food for the table.

    This lot will hopefully provide me with a warm and cozy home with minimal utility bills and food security. If we have another pandemic and/or financial crash, I should be able to manage on the state pension without the fear of the 'heat or eat' choices that many people have when times get hard.
    Posted By: Pile-o-StoneMy plan is to build a highly insulated and highly air tight eco house with private drainage, rainwater recycling and perhaps a borehole for drinking water (or spring depending on how lucky I am with my land purchase).

    Off topic but does this mean you will be abandoning (aka selling on) the 'pile of stones' you have just renovated and will be starting again?
    I agree with greenpaddy above - it would be worth digging the ground level inside the greenhouse. Take care with just levelling off (moving the high end to build up the low end) because you because too much of a step up or down will be a pain. But a raised bed on the high side made by levelling off would work)

    I would not build timber frame wall in a greenhouse. Greenhouses are wet damp places and whilst you get timber frame green houses these have open timber which has a chance to dry out. a TF wall with covered timber framing will not dry out - it will stay wet and rot.

    I would be nervous about rammed earth or tyre walls because neither are water resilient and will quickly melt from the watering of the plants.

    Health warning - I am not a SE or a builder but my building degree is from the university of Life. But for the wall I would use 200mm hollow concrete blocks for the wall filled with a weakish concrete with both horizontal and vertical rebar. Have good returns both ends (as per your plan) but I would add two piers equally spaced along the wall. Foundations should be to suit the ground conditions and I would put vertical rebar in the foundations to tie into the wall.

    Building a steel frame greenhouse would be an option and if you can weld it is an easy construction (bolt up is possible but it is slower and the joints are not as stable) Foundations would be a lot less than for a concrete wall but I'm not sure about the relative costs if steel/glass vs. block wall. Even on a north wall you get useful light through the glass and whilst you don't get the thermal mass of concrete 2 - 3 water filled barrels can provide the same function and will give up to temperature water for the plants (they don't like a cold bath any more than I do) Probably worth doing the costings. When I was in the UK you could get horticultural glass that was cheaper than window glass, I don't know if it is still available. Think about using polycarbonate or tempered glass for the roof, either for reasons on safety. I would used ordinary glass for the sides.
    Bit left field, but you can often get cheap/free secondhand panels from precast sectional concrete garages. There are a few on eBay for £0.01, buyer collects. The panels stand up next to each other joined together with bolts and are propped up by their end returns.

    They probably wouldn't work as earth retaining walls, so you'd want to dig back the bank to make a stable slope.
    Thanks for all the suggestions. I was particularly taken by the rammed earth in tyres idea. However, I recently had to move my hens into greenhouse 1 on account of bird flu. The rats followed them, digging burrows under foundations that I thought were too deep for rats to dig under. I've moved the hens elsewhere now, but the rats remain a problem. I can imagine that if rats started nesting amongst the tyres, I'd never get rid of them.

    I've looked closely at the structure of greenhouse 1, and though it's a few years old and I didn't think to put drainage at the footings, it seems stable. No cracks anywhere. So I think I will after all construct the base like that, with raised beds against the north wall, about a metre high. The raised beds being formed with blocks, and the blockwork of the north wall and the raised bed tied together by probably three connecting walls.

    I'll definitely put drainage in this time, and hopefully enough ballast around the footings to make rat burrowing unlikely.

    From about 2 feet above the ground to the roof, I think I'll go with timber frame. As someone suggested, I can use second hand EPS to insulate it. There happens to be a skip load of it nearby where some new build flats are having to be refurbished on account of leaking roofs and walls. If the timber frame is suitably insulated, I don't think it will get damp, as the dampness in the greenhouse comes from condensation on cold surfaces.

    Hollow concrete blocks are about three times the volume of standard blocks, but also three times the price at the builders merchant down the road. And then, they need to be filled with weak concrete mix. So they seem a more expensive option than just laying standard blocks down sideways (making a 220mm wide wall). I don't think I need to add steel given the support from the raised beds and the interconnecting walls, which would I think be a reason to go with hollow blocks, so unless I'm missing something here, I'll go with standard blocks.
    Posted By: Peter_in_Hungary
    Posted By: Pile-o-StoneMy plan is to build a highly insulated and highly air tight eco house with private drainage, rainwater recycling and perhaps a borehole for drinking water (or spring depending on how lucky I am with my land purchase).

    Off topic but does this mean you will be abandoning (aka selling on) the 'pile of stones' you have just renovated and will be starting again?

    I'm still renovating. :cry:

    I sometimes feel like I'm in one of the recent Grand Design episodes where it took them so long to build the large family house that the kids have grown up and moved on and the builder now just needs a bungalow for him and the wife (or just himself in one of the recent episodes). My renovations have been on-going (though a bit 'on and off' when funds didn't allow) for the past 10 years and we have had one daughter leave the nest and the other daughter is now 18.

    We are planning on completing the current projects on the house over the next couple of years and then selling up and starting our next adventure with a smaller 'pile of stones' more suited to what we want out of the last quarter of our lives. This house has been a great learning curve though and got me interested in eco building.
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