Green Roof

August 11th. Planting the roof.

The roof has been taking longer than expected. I was hoping to finish around the 20th July - so running about three weeks behind schedule. Adding the skylight was a late addition to the plan, and other aspects have taken more time because of the size of the roof. At around 55 square metres, it is a giant; you could have a game of tennis up there.

On my last blog, I showed pictures of bulk bags of cockle shells and 3 - 8mm leca, and of the shells spread on the roofing membranes as a drainage layer. After completing the shell layer, I put a single line of flint cobbles around the roof deck. They are sitting on a layer of RFG to raise them up to be visible over the retaining boards.

Then it was time to mix the substrate - the lightweight growing medium for the plants. I was aiming for a substrate thickness of 2 - 3 inches (50 - 75 mm). My ingredients for the substrate mix were: 

• 3 - 8mm leca. These are fired clay particles used as a lightweight aggregate or insulation. They look like cocopops.
• Coir fibre. Sadly, I took no photos of the coir fibre before mixing. It arrives in 5 Kg blocks the size of a large shoebox. You add water to reconstitute it, and after you have added a lot of water and forked it over, you get a heaped wheelbarrow full of fibre from one block.
• Expanded Perlite. Perlite is a volcanic glass with a high water content. When heated, the water evaporates and leaves a lightweight honeycomb glass structure. I used a 3mm grade.
• Sharp sand
• Crushed rubble. I put a mix of everything in here: all the remaining RFG, some mortar from the demolition of a garden wall (source of my stem wall bricks), crushed brick. It all had to be crushed with a tamping rod.

The mix evolved as I went along, mainly to make full use of the materials I had bought. It started out as: 3 leca, 3 coir, 1 sand and 1 perlite (= 4 buckets); by the end, the final mix was 2 leca, 4 coir, 1 sand, 1 rubble and 1 perlite (4.5 buckets). The whole roof took around 55 mixes, roughly 1 mix for each square metre of roof.

Crushing rubble

Loading the forced action mixer with coir.

Two or three minutes later, filling sacks with well-mixed substrate.

No, I haven't got a hoist!

Using roofing battens on edge to regulate the depth - approximately.

Last strip of substrate. Actually, you can see I have already planted some of the roof here, but I'm going to go back a step to talk about the plants.

Plants: We want some drought-resistant,  ground-covering plants for the roof, to hold the substrate in place and green the upper surface. Sedum is recommended. You can buy beautiful ready-grown sedum mats and unroll them on your roof, but with 55 square metres of roof to cover this would cost thousands of pounds, so we have another plan.

We asked our friends what they had. In some cases, we were even cheekier and asked people we didn't know if they could spare some plants! We were very kindly given a large tray of creeping thyme, a small tray of semper viviens, and as much wild sedum as we could dig up.

This is our source of sedum. It's a concrete road circa 1941 on an old USAF Norfolk airbase, currently used for storage of potentially recyclable materials. We bagged up a small proportion of this.

                     

      

Then we divided the clumps, and planted plugs of plants at 9 inch separation over the whole roof area.

Until it looked like this:

With thanks to the roofing crew: Chris, Adam & Izzy. 

Roof, Doors

22nd July

It's a couple of weeks since I have posted, but work has been continuing. There were a few days rest after I got the edpm cover on the roof.

I've added eight of these storm straps linking rafters to the wall plate, which I hope will keep the roof firmly attached in a gale. The roof weighs at least a ton already, and will increase to over 3 tons with substrate and plants, so it's hard to imagine it going anywhere, but it is almost 60 sq metres, so quite an area to catch the wind.

This is a job I should have done before building the walls! I've made a door frame. The posts are 3 pieces of 4 x 2 timber, and I've put a 6 x 2 beam under the wallplate to try to stop it sagging from the weight of the roof above.

 Door liners added:

                                       
 My wall sections ends are a bit ragged (which is why I should have added the frame before I built them) so I have closed the gaps with a bit of feather edge cladding:

...................with sheeps wool insulation stuffed into any gaps.

Apologies for photo quality - it's hard to get a decent snap in bright sunshine.

Then the doors. These are recycled patio doors from the house, installed in 1975, internalised during the 1980's and removed last year. I need to reduce the height by around 150mm, and the width by about 10mm, hang them plumb and square.

It may not look much, but the frame and door hanging was a week's work.

So, do you like my skylight?

If you are reading this because you are interested in sustainable construction, then you probably don't think a lot of it. It's a twin wall polycarbonate dome skylight on a 150mm pvc upstand

I have had to cut a hole in the edpm pond liner, lap it up the upstand and apply flashing tape to try and keep it watertight. I'm way out of my comfort zone here! I would of course prefer something made of wood, glass and linseed putty, but I spent many years in houses with leaking skylights, and I think the chances of one that's been fitted by me on what is practically a flat roof keeping water out are very slim. The dome is like an umbrella, and is better-designed than anything you could make out of flat glass for this application.

28 July Weather - hot, dry and windy. POOSHers: - haven't seen any since June 14th.

Roof work continues. I have been gluing down the edges of the pond liner with contact adhesive, a slow, difficult and messy job made difficult by strong winds. 

Followed by attaching a retaining board around the whole roof. I have used 6 inch gravel boards, tanalised. I made a compost box with these a few years ago and they are very durable when in contact with damp vegetation.

By some trick of camera colour compensation, the next photo does not look very different. In fact, the one above shows a black edpm liner, a synthetic rubber waterproof membrane. The photo below shows another layer of light grey geotextile membrane which I have used to cover the edpm and protect it from sharp stones, roots etc. 

 I have run the geotex up the retaining boards. It is water permeable, so water will drain off the lower edge of the roof and the substrate will stay where it is, unable to pass through the geotex.

I have bought a bulk bag of cockle shells - a food industry by-product; and, below, an even larger bag of leca (expanded clay).

These are both lightweight materials that I will be using on the roof for the plants to grow in, the substrate.

It's a layer of shells first, to act as a drainage layer:

I've also been using some leftover recycled foam glass gravel around the edge, and some 20mm gravel that was left over from the foundation trench fill. Pretty much anything can go on!. Crushed bricks, old mortar, sand, soil, all mixed with the lightweight aggregates I have bought: leca, perlite and coir fibre.

Roof Carpentry

Monday 16th June. Weather: cool, breezy,

After a few days break, the next job was to get the permanent roof on. My lovely volunteers have all gone home and I am working by myself again. We are stuck in a cold, wet airstream whilst the rest of the country is having summer, so it's all a bit of a change from the last 3 weeks.

I have added the rafter bearer in the pic above - the piece of 4 x 2 timber on top of the wall plate. It has taken about three days! 

I had a bit of a problem after the compression of the walls last week. The compression was uneven, and the wall plate was not level: the front wall had a concave dip in the middle of about 30mm, and the back wall was convex by about 20mm. To get the rafter bearers level, I have carefully sculpted them (with a power saw) to reduce their thickness at the ends of the front wall and in the middle of the back wall. It has also taken a lot of time to measure out exactly where to fix them so that the span is constant and the rafter spacing is regular and symmetrical.

The weather hasn't helped. I need to take the covers off to work, but put them back on again when it rains, which was a few times a day for a while. And it's been windy, and loose covers flap around.

Thursday 19th June. Weather improving, some sun, less rain

But by Thursday the weather was brightening up, and I was ready to make some rafters. I had made myself an additional problem by misjudging the height of the temporary roof. The front was too low, and in the way of the rafters. I have raised the whole front of the temp roof by propping it up on the wall plate..................

....................which means that the front line of columns (including my tool station)....................

..................can now go.

Columns dismantled. I am using the 4 x 4 columns on the rear wall plate to get a slight rise to the roof.

This is a first: using my rafter square to mark out rafters! Clever tool! I used to think it was just a set square with a ruler on each arm. I have a rise of 250mm over a rafter run of 4.3 metres, which gives a pitch of 1:17, or about 3.5 degrees.

First rafter takes shape................

.................and seems to be a good fit. Only 23 more to make. Each rafter weighs about 30 kg, so they are difficult to move and work on solo, especially hoiking them up onto the walls.

Saturday 21st June. Weather: warm, dry and sunny. Working solo

Gang-cutting notches in rafters. I'm loving working in my new workshop already. 

Tuesday 24th & Wednesday 25th June. Mainly fine but with occasional showers.

However occasional, showers are difficult to work around. It's currently taking around 20 minutes to uncover the roof, and around 40 minutes to cover it up securely again. I have been just peeling back a corner here and there to start constructing the permanent roof

Rafters at eaves with noggins for stability. I have bought 26 pieces of 200x47mm timber 6 metres long.  I had planned the rafter length to be 5650mm, but I realised that if I reduced this by a smidge to 5640mm, then instead of having a pile of useless offcuts about 348mm long, I could have 26 very usable offcuts 358mm in length, and make some 353mm noggins out of them

Over-lookouts at eaves. This may not be the English name for them; I've been reading an American carpentry manual. The end rafter is overhanging the side of the building and needs quite a lot of support. Lookouts transfer the weight of the rafter and the roof above to the four rafters next to it. Over-lookouts hang on the neighbours and give cantilever support to the eaves rafter; I have made five at each end of the roof. There will also be three under-lookouts that give the eaves rafter some support from below, sitting on the wallplate. These will transfer some of the weight of the roof to the short walls rather than have the whole roof supported on the two long walls.

And the first pieces of roof decking go on at the corners. The decking is sitting on the permanent roof frame, anything above this level is the temporary roof.

Thursday 26th June. Weather - we're on a promise of an entirely dry day.

I've had a couple of dry days in the last fortnight, but these have been days when occasional showers have been forecast but not materialised. Today the met office is saying "No rain. Definitely." It's going to be a long day's work!

9.15 Covers off:

10.15: Temporary roof dismantled: 

My first view of the finished building side elevation..........

....................and of the interior without pillars.

Pile of wood for recycling. 

Actually, I've already taken most of the 4x4 or 100x100mm pillars in this photo. They are going to be used to complete the roof riser on the back wall, shown below

13.00. Riser wall completed. I have left a small opening in the middle of the riser which will become a ventilator

14.00. Five rafters to still to do.

A clearer view of the over-lookouts:

Pile of noggins. As well as the 8x2 offcuts, I have also sawn up most of the 6x2 timber that I used as rafters in my temporary roof.

16.20. Quite a lot of noggins in place. It's a long job. I think I might need some more - perhaps five for each rafter interval.

17.45. So- what's this a picture of?

Is it a bird? ..................................No!

Is it a plane? ................................No!

Hang on. Actually, it is a plane of sorts. In the absence of any lifting machinery (or superman), I have resorted to using an inclined plane to get my sheets of 18mm OSB up on the roof. I think the Egyptians used this technique to lift their heavy stuff.

I know a sheet of OSB isn't in the same league as the stones in the pyramids, but then I don't have a gang of slaves to help me. It was a bit tricky getting a photo of what was going on here, as I couldn't lift and photograph at the same time. I put a ratchet strap around the sheets, one by one; tied a rope to the strap; stood on the roof with the end of the rope and hauled them the inclined plane, which was made from the last five rafters.

(Note on the pictures above. I've shown these to a couple of people, and they have mentioned the "big roller" on the scaffolding, so thought I'd better tell you what it is. It's not a roller for the inclined plane - it's my pond liner, which I am going to use to waterproof the roof.  It weighs about 60Kg! It arrived a few weeks ago when I had lots of help here, so instead of leaving it in the store for me to try and manhandle up onto the roof by myself later, I got my POOSHers to help lift it up to roof height ready to unroll on the deck when it's ready.)

20.45. (Good job it's midsummer.) Nearly all the sheets in place. They're not screwed down yet, and there is still work to do beneath: under-lookouts, noggins etc. That will have to wait for the next dry day

21.45 Covers back in place. Time for a drink!

Monday 30th June. Working solo, weather dry.

This is the third week of roof carpentry and the sixth week since we started working with straw. Unusually, and thankfully, we have a dry forecast for the week. You will remember that last week, I hurriedly got the roof deck into place and covered up, but left quite a lot of work unfinished in the the structure below.

I nailed a few more noggins into place, three per rafter gap making 63 in total. However, the rafters are nearly 6 metres long, and I was concerned that there was still potential for twisting  at the eaves. I had used all my 6 inch and 8 inch timber, but still had a lot of 3 x 2 inch timber left from the temporary roof, so I decided to add diagonal cross-bracing to the rafters instead of noggins.

After a bit of trial and error, and a lot of measuring and re-measuring, I got my chop saw set up to cut the struts shown below, and then cut 84 of them.

A pair for each rafter gap where they cross the walls

Using a brick line to get the roof deck sheets accurately lined up.

Last week when I got the roof deck sheets in place for the first time, I realised how dark the workshop was going to be. I had been putting off a decision on a skylight, but quite quickly came to the view that one was needed. 

Forming an opening with joist hangers. With a possible skylight in mind, I have bought and made an extra two rafters, and I am using these now to double up the rafters either side of the skylight.

 Completed skylight opening 750mm x 750mm, from above.......

......and with a matching "trap-door" cut out of the deck sheet.
(I have battened round the opening and replaced the trap-door for now, until I have a skylight to fit.)

Let there be light! The skylight opening from below.These jobs have taken 3 days, and it's now Wednesday evening.

Thursday 3rd July. Working solo, weather sunny, dry and hot. 

My photo shows a 50mm x 18mm roofing batten, recycled from the temporary roof, which I have cut in half lengthways. I thought this might be a job for my table saw, but it was making heavy work of it. The circular saw was difficult to cut accurately with, and I ended up cutting around 16 metres of batten with a jig saw. The roofing battens are the only timber in my building that has been pressure treated. It's hard to find untreated timber in this size.

I am using these timber sections to make a drip-strip around the entire edge of the roof deck. The picture above is a close up of one corner of the roof deck with the drip strip attached in on direction; the picture below shows how the waterproof membrane will wrap around the drip strip. The idea is that water will run off the roof, down the membrane to its lowest point, then drip off without getting any on the roof timber wet.

I have also screwed down all remaining deck sheets today. There are 20 sheets,  and 28 screws per sheet.

Friday 4th July. Working solo, weather dry, sunny & hot

The carpentry is complete, time to get the waterproof edpm membrane. This is the heavy roll that has been sitting on a high scaffolding hand rail for a few weeks.

But first, it's a layer of geotextile backing. This is to protect the edpm from any sharp projections on the roof. The fibres catch on the SmartPly, making it difficult to slide to adjust it's position once on the roof. I have been using a tarp to unroll and position it, then whipping the tarp out and brushing it flat.

 Geotextile layer complete.

 Makeshift ramp under the edpm roll

Successfully lowered and rolled onto the roof.

First attempt - following instructions on the supplier website - turned out to be the wrong way to do it.

Second attempt was a better fit: 6 metres of concertina fold edpm laid down the centre of the roof.

And here's the roof fully covered and waterproof.. No more worrying about whether the tarps will hold out and keep the straw dry!

I had originally thought that I might leave the roof like this. But: the sunshine was intense today, and the black edpm was so hot that you couldn't touch it. I thought it better to unroll the white tarp on top of the edpm to reflect some heat. It was also helpful to tie down and secure the edpm against wind.

This is the end of the "Roof Carpentry" section. This is also the end of the "weekly diary" entries here; from this point on, work will be a little more intermittent and my posts will also be less regular.

Work remaining on the roof is: buy and fit a skylight; cut the edpm and make a skylight flashing. Secure the edpm around the edges. Make an upstanding roof edge all round. add around 6 cubic metres of lightweight substrate and add plants.Fit guttering and downspout to front side. Work remaining on the building is: doors, windows, internal and external plastering and electrics.