Attic Shaped Studio

[Starlight]

Source of the postCheck with Starlight to see if his silencers are of a similar robustness.

Yes, mine ar two layers of 18mm MDF. As boxes they are sturdy and almost as heavy as Jennifer's but, if I have read and understood correctly, they will be mounted quite differently to mine; it seems that all 50kg will be pulling on the vertical connection and the length of the boxes look long enough that it will create a significant downward force. Something inside me is a bit nervous.

The two main benefits of OSB over MDF or plywood are that OSB-3 is suitable for exterior use and that its shear strength is higher than the alternatives. A minor downside of OSB is I get more splinters in my hands from OSB that any other wood product. Overall I like it and like working with it. I have 36 OSB boards from two deliveries and every one is perfectly flat. MDF has no grain so unless it has bee stored damp it will be fine. Sadly, I like playwood but I have not had a single flat board on this project, every one has been bowed to some extent.

I have 15mm of OSB board above the 2 plasterboard layers on my inner room ceiling which means that anything that hangs from the ceiling is reliant on the OSB's shear strength, of which one silencer box is laid horizontally and has support underneath along only one edge, so the 4 screws holding the other side up are holding up a fair proportion of the 38kg baffle box. For interest, see the nearer silencer in the last photo in post 65 of my build, here. The farther box is held up along two edges and that helps, greatly reducing the downward pull of the box on the ceiling screws.

+1 to Gareth's comment on Jennifer's Sketchup skills.

[endorka]

Source of the post Hi
I can also recommend speaking to Just Fans about the fan you'll need, they were very helpful for me. I settled on: https://www.justfans.co.uk/awv-external ... p-121.html

Thanks Gareth, nice to know they offer good service, I'll give them a call. They have the fan I'm after and some of the accessories as well at a fair price; https://www.justfans.co.uk/silent-500150-p-1906.html

I don't know if it's of any help, but I'm going to have a load of the 'proper' duct liner spare from my build. The company that make it in the UK make it to order and it's a minimum size of 15 meters long. It even came on a pallet! I won't even need half of the roll, I don't think, so if this is of any interest send me a message.

Absolutely of interest, I have send a message

Thank you for the Sketchup compliment. I still find it tricky to use, on the positive side it has been useful in generating some good design insights and also revealing some flaws before buying materials.

Cheers!
Jennifer

[endorka]

Source of the post Yes, mine ar two layers of 18mm MDF. As boxes they are sturdy and almost as heavy as Jennifer's but, if I have read and understood correctly, they will be mounted quite differently to mine; it seems that all 50kg will be pulling on the vertical connection and the length of the boxes look long enough that it will create a significant downward force. Something inside me is a bit nervous.

That was very useful to see how yours were installed thank you. My perhaps naive understanding is that there will be two main components of force acting with the wall mounted method. First is the vertical sheer force, and with Gareth's analogy to the kitchen cabinets and your mention of the OSB-3 having good sheer strength, I am confident that aspect will be ok.

The other force will be centred around the fulcrum of the assembly (the moment of force?). The centre of this will be where the very bottom of the silencer assembly where it meets the wall OSB panel. The force preventing it turning is applied by the lever action of the "dog ears". This is the area of unease and uncertainty I think. The longer these ears though, the less force required, so I'll make them a bit longer just in case

Fortunately I can test the silencer & knee wall assembly as one piece before installing it!

Thanks again,
Jennifer

[Starlight]

I think my nervousness is because my memory goes back to physics lessons at school and diagrams like this one:

I have two silencers that are standing upright, Their load would be measured as a in the diagram. My other two are lying down; their load would be measured as L. For the same weight L has a stronger downward force than a. I remember that if L is twice the distance of a then the dowward pressure is twice as much.

Jennifer, I am under the impression that a kitchen wall cupboard will have a reach from the wall of about 300mm but that your silencer will be significantly greater, and that means the downward pressure will be greater. I would be concerned that over time the stress on the upright OSB panel your silencer is attached to will weaken or distort.

I am assuming that you are wanting to avoid contact with the rafters. If so, have you considered adding a beam between the rafters (my dark brown addition to your picture below) and use an acoustic hanger to bear the weight? I know we have talked about AMC in Spain where I got mine. That would relieve the OSB from having to be a cantilever bearer of all 50kg.

It is possible I have not properly understood what you are trying to achieve and what you are wanting to avoid.

[endorka]

That's a brilliant analysis, thank you, and you've understood exactly what I'm try to achieve including avoiding contact with the rafters.

Your suggestion of the acoustic hangers is spot on, I hadn't thought of that. I had initially planned to sit the silencers on isolated feet on the floor joists, but fitting and balancing the weight of them would be a major PITA.

One thing I am trying to avoid is fitting tricky stuff at the end of those spaces. They are pretty narrow and inaccessible, and cutting through the balcony walls is a big no-no! But the hangers as you suggest would be doable without having to do any of that.

To fit the filter box shown on the inlet silencer I'm going to have to cut a hatch into the plasterboard ceiling below. The exhaust silencer on the other side of the balcony isn't so bad as I can get access to one side through the eaves.

Updated plan as a precaution: build a silencer with longer dog ears, mount it to the wall OSB board but not in place. Keep it in the correct orientation elsewhere for a month, and see if there is evidence of sagging. If so, sort it out.

Another possibility might be fitting stiff reinforcing bars / planks across the face of the OSB at the top and bottom where it joins to the silencers. Grey bars in the picture below. There will be another player of plasterboard on top of the OSB so this would be easily concealed.

Thanks again for all your help,
Jennifer

[SoWhat]

Greetings Jennifer,

Another possibility might be fitting stiff reinforcing bars / planks across the face of the OSB at the top and bottom where it joins to the silencers.

I was going to suggest this. With the plasterboard going on top, you might put those on the vertical as well as the horizontal as you've pictured.

Also, exterior/deck screws (T25 heads) work really well for these sorts of projects. But you probably knew that.

All the best,

Paul

[endorka]

Source of the postAlso, exterior/deck screws (T25 heads) work really well for these sorts of projects. But you probably knew that.

I had no idea of that at all actually, so thank you for the heads up. It seems we have two common options here in the UK, the Torx head (I think that is similar to the T25) or square heads. Presumably these give far better transfer of torque than the usual screw heads?

Cheers!
Jennifer

[SoWhat]

Basically the same options here in the US. Yes, PLENTY of grip: very positive feel when being driven. Kind of the same feel as TAPCON anchors going into concrete.

T25 is a Torx (the "T" in T25). I like the T25s better, if for no other reason than the 2" long T25 bits for the impact driver seem to be more ubiquitous.

[garethmetcalf]

+1 for torx head screws. I will never go back! Screwfix sell a very reasonably priced set of varying sized torx screws that comes with the necessary t20 and t25 attachment.

Gareth

[endorka]

This one here? Should've bought something like this years ago instead of buying all these individual packs over time!

https://www.screwfix.com/p/turbo-ii-tx- ... -pcs/7282h

[SoWhat]

An 850-piece assortment should get you by for awhile...

...although if you use one or two sizes frequently, it pays to buy them by the high-count box (if they are sold that way in the UK; they are here in the US), as you won't be paying for the storage case or the screw sizing you might never use.

20 quid for 850 does seems like a good price.

[Starlight]

What a coincidence! I had been reading about pocket hole jigs and seeing Jag94 use one in his build I bought one. It turned up with a T20 piece and so this morning I ordered a box of torx pan head screws. I like how we can learn from each other.

[endorka]

Absolutely, I've learned so much from others here, it's great. Loads of it applicable to general DIY jobs as well.

I bought one of those pocket hole jigs a few months ago, they're well handy aren't they? This one used square head pan screws though, I had to order a screwdriver bit specially for them.

Cheers,
Jennifer

[ScotcH]

Ha! You peasants without readily available robertson construction screws

[Jag94]

Torx and square head screws are the absolute best. I have come to hate standard philips head screws now.

Jennifer, my pocket hole jig came with a LONG square drill bit specifically for the pocket hole screws. I'm surprised yours didn't.

Also, I'd recommend getting good quality T20 and T25 bits, and then buying the screws in larger quantities. Here in the states, Dewalt and Millwaukee make really good quality bits that click in to impact drivers. I bought a pack of each and they last a REALLY long time, and can handle the torquing of those screws into all kinds of wood. They were not very expensive, and absolutely worth the money. DRILL BIT