Astrokev

That's a good point Chris. The total weight will be taken by the 3 cross-beams, each of which will be supported at the ends. Some of the load will therefore be directed down through the walls of the main structure, reducing the load in the middle span of the cross-beams. There's probably an engineering formula to calculate the load in the middle but that's a bit beyond my knowledge. I used the same technique with a garden shed rebuild a few years ago and the apex beam can easily take my full body weight. I'm probably worrying unduly, but may redesign anyway just to be sure. Overengineering - I love it!

Speaking metaphorically of course ?

...and an air-con tube filled with a ton of concrete. My back is still aching!

Sounds like a plan. I guess the only risk is that the blocks may crack when drilling, but sounds workable.

Well, the planets finally aligned and I laid the EPDM today. With hindsight I think it may have been better to choose a cloudy day. I initially took my shoes off to walk on the roof and when the sun came out the rubber was almost too hot to stand on (brought back childhood memories walking across boiling sand on the beach!). The water based adhesive was fairly easy to work with, although it was a little too quick to dry in the mid-day heat. The contact adhesive was horrid, drying almost before I could get it off the roller or brush. Once I got used to how it handled I managed OK though. First job was to fix the corner pieces (see several posts ago for images and logic for this). A bit tricky to slide the rubber between the roof and the side rails without the 2 adhesive coated surfaces touching until I was ready (manoeuvring 1.2mm rubber in a 2mm gap was a bit tight ?), but was surprised that I managed to get them fixed first time without problem. Images below. Once dry I trimmed the top edges then cut and stuck down the main sheet. The lower corners proved as tricky as I suspected and it took ages. By the time I'd finished in the early evening I was too shattered to remember to take pictures so will post these tomorrow. Just a bit of tidying up to do and put up some kind of barge board along the rear edge. For the sides of the track rails, rather than use clout nails, I'm wondering whether to use an aluminium strip which would be thinner (than a timber batten) and may look more attractive than nails. Clout nails would work fine I guess so I must think about that one ?

Thanks Chris. Have you noticed any deformation of the apex beam across the obsy due to the weight of the roof? I'm wondering whether I need to strengthen my beam and increase the clearance of this over the fixed beam separating the warm room and scope room. My current design has a clearance of around 30mm.

Looking good. Interested in seeing how you will join these together.

Yes that's a thought. I did that many years ago to increase the rigidity of a kitchen worktop that spanned a washing machine and tumble drier! Worked quite well as I recall.

Thanks Gina. Yes, mine will have a gutter on the south end which will hopefully prevent water getting in when I open it, and may also catch other bits of debris. I must give this some more thought though to make sure I position the gutter correctly to act as a trap. Regarding the risk of the apex beam deforming, I'll relook at the clearance. I may be able to increase this slightly, although I think I'm pretty close to the 2.5m limit ?

Thanks nightvision. That sounds an innovative approach. I've not heard of carbon tape so must do some research ?. I'll also relook at the dims of the beams; I may be able to increase these slightly.

Thanks James. No, that's a fair point. Sadly, there's a biggish hedge to the West and a fairly tall Lailandii (both owned by next door neighbour) which tend to shed all kinds of rubbish. I gave this a severe trim last year and have just had another go at it, reducing the height a little bit more hoping that the neighbour won't notice, but there's only so far I can go! There's also a huge pine tree ~25m away which sheds needles by the ton at certain times of year. I will be installing a gutter at the bottom of the slope which may help reduce the risk but I'll certainly give this some thought! I think @yesyesused this design, so would be good to hear from him when he's next on the thread?

My thoughts are now returning to the rolling roof. Once the EPDM on the warm room is down (hopefully tomorrow), this is the next job. This post is to ask folks views on whether the design shown below will be rigid enough across the width of the obsy. Pic 1 is a general 3D view. Pic 2 is a sectioned orthographic view looking along the apex, with the side panels removed for clarity. Key = Parts shown in green, yellow and blue are the rolling roof. Red parts are the position of the V wheels. I've only shown a couple of green joists for clarity. In total there will be 6 or 7 (haven't decided yet). The pale grey timber is the fixed dividing beam separating the warm and scope rooms. The yellow and blue beams span approx. 2.3 m unsupported apart from at their ends. For the yellow beam, my plan is to use 2 lengths of 45x95 timber screwed together, making a beam 95 (vertical) x 90 (horizontal) in size. For the blue beams, one is 120(V) x 45(H), the other 95(V) x 45(H) Now that I've felt the weight of the EPDM, although the load will be spread out, I'm concerned that the beams may bow in the middle over time. The separation between the grey dividing beam and the yellow roof apex beam is about 30mm, so there's not much room for movement in the beam if it does start to bow. What do folks think? Do I need to consider a different design to increase rigidity and reduce risk of bowing? Thanks

The weather has improved slightly so I had to roll out the EPDM to check dims. Good news is that all is well - in fact it's a little larger than I ordered so should remove risks from my measurement errors. I've cut the piece I need for the warm room but will probably leave this until tomorrow now, when I have more time. I'll mark up the roof this afternoon and finally decide which areas I'll use contact adhesive and which WBA. A question to those who've used EPDM - it comes with a fair amount of powder covering the surface which they say is to make handling easier. Does this impair adhesion at all, or should I try and remove it before applying adhesive? Thanks

Thanks Kev, that's kind of you to say. Feel free to borrow as many ideas as you want - the reality is that these are not really my ideas at all, as I pinched most of them from other builds! I think that's the whole point of this forum - to share ideas and experience so we all benefit. I have certainly been inspired by many builds over the last 5 years or so and have been cherry-picking ideas from others along the way for when I eventually (and it took some time for me to start in earnest) made a start. The main build that inspired me most was @yesyes, and I recommend you dig out his build from a few years back, but others include @RayD, @Gina and @Malc-c. All excellent builds. I'm enjoying the project and like to share as much as I can. If others enjoy following my build as much as I've enjoyed following others, then job done ?.

Well, the replacement EPDM has just arrived..... and now it's started to rain. The BBC weather app gives a 2% chance of rain in the next hour. Huh! My luck is doing too well at the moment ?

I've been playing around with how to fit the EPDM around the corners of the warm room roof. I believe the traditional way is to use folds similar to when making a bed. Unfortunately, this doesn't work with my design, since I want to cover both the roof and the adjacent rail beams with a single piece of rubber. Because the roof slopes, the angles of the roof and rail are different and trying to fit a single piece snugly around all the timber just doesn't work. Despite playing origami with some EPDM off-cuts, I've concluded that it's impossible to get a good fit around the OSB without cutting into the corner, which would obviously risk water getting to the OSB. I should have considered this more fully when I designed the roof. So, here's my solution. I hope to first fit a corner piece (2nd pic) to give good protection of the roof edges ( I say hope because once the rubber is glued-up it may all go horribly wrong when trying to fit it into the c.2mm gap between the roof and the rail). Then the main EPDM sheet will be cut and folded as shown. It's difficult to illustrate this clearly in 2D but hopefully you can see what I mean in the sketchup diagrams and the feeble photo of me trying to hold the rubber with one hand. The end result gives much better protection of the OSB - I hope.

Sadly not Chris. TNT collected the wrong one a short while ago. There will be some left overs, and I've got a fair bit left from my pond revamp last year. I'm sure these will come in useful for sealing the nooks and crannies to keep the worst of the weather out ?

Rubber4roof update. The very nice man was hugely apologetic (as expected) and is to send out the corrected order today. I guess you can't expect more than that. Looking forward to cutting some rubber ?

Not much action on the observatory today then after all, but I did put up a bit more of the breather membrane around the warm room. Beginning to look quite cosy in there now and starting to get a feel for what it will be like when it's fully walled-out. The full obsy image looks a bit of a bomb site. The EPDM on the roof is a patchwork of off-cuts from last year's project of relining the pond and is just to keep dew off the roof. Taking no chances! The bent uprights in the middle pic are camera distortions - honest!

Yeah, it's the lost time that annoys most. Even though I'm now retired and theoretically have more time (I honestly wonder how I ever found time to work before retirement), trying to align free time when the weather is decent isn't easy!

You're right there. In order of total cost to date: 1st=Timber. 2nd=EPDM. 3rd=V track and wheels. 4th=small metal brackets. BRACKETS! Who would have thought it! I'm obsessive-compulsive when it comes to lists n things. I've got so many spreadsheets and pivot tables related to my astro stuff and obsy it worries me sometimes. Being a retired scientist probably explains it! Ignoring the pier, actual building costs are currently around £1700. I don't expect much change out of £2500 when it's finished. But as you say Gina - it'll be well worth it!!

Well, Saturday was wiped out due to my daughter hurting her ankle and us having to spend the morning waiting in-line at the walk-in medical centre. Fortunately she's OK and will fully recover in 4-6 weeks. So, this morning was the big day - unwrapping the EPDM and getting it stuck on the warm-room roof. Here's a picture of the said EPDM stretched out on the lawn to check it over. Lovely you might think - and that's what I thought until I got the tape measure out, just to check. They wouldn't send me the wrong stuff, would they? Well, it seems I was wrong, and yes, they have sent me a different size to what I ordered. I ordered a length off of the 3.53m wide standard roll. They got the length correct, so are able to use a tape measure, but sadly they seem to have cut it off of the wrong roll, sending me the standard 3.05m wide material by mistake. How cross am I? I'll leave you to figure that one. To add insult to injury, in a separate order they also sent me a 9" roller when I ordered a 4" mini-roller. I forgave them that as it's only a few quid and not worth the hassle of returning it, but a >£200 EPDM order is a different thing. So, tomorrow I'll don my Mr. Angry hat and there'll be a very irate phone call to Rubber4roofs!

I shopped around the area but, to be honest and all things considered, Wickes seemed to be the best. But you're right, the costs rack up. I'm keeping a complete list of costs for everything that goes into the observatory, but beginning to wish I hadn't started this - it's getting quite scary ?. Good job the build has taken a long time to get to this point, to spread the cost!

Looking good. How did you find the quality of the long joists? I had them spread out over half the floor at Wickes to find the straight ones that weren't twisted! I'm OCD when it comes to buying straight timber. I think RayD called it playing giant Jenga. They must love me at Wickes ?

Spent the morning checking out a beautiful second-hand scope. My will-power collapsed and I collect it next week. Happy bunny! By the time I got home the day was largely gone, but found time this evening to make a bit more progress. OSB cut and screwed in place on the warm room roof. Hope to do battle with the EPDM tomorrow. Have to admit to feeling a bit nervous; never used it before and the bottom corners look a little tricky. Contact adhesive seems pretty unforgiving if I don't get it right first time. Watch this space...