Strong alternative to chimney corner bracket

I want to put a satellite dish plus motor on a tenement chimney, but unfortunately one south-west corner of the chimney is already in use for someone else's dish, and the other south-east corner is above the sloping part of the roof so is not accessible (except by the use of scaffolding).

The chimney stack is wide (common to about 16 flats) and measures 3.4 metres east-west by 1 metre in the north-south direction by maybe 1.5 metres high excluding the chimneys. Part of it is above the flat section of roof.

My understanding is that the best way to attach a dish is by the use of a corner bracket plua a steel clamping cable around a chimney stack, but that seems difficult to arrange in this location.

TV aerials are sometimes bolted to the side of a chimney stack, but presumably for a dish that might be a poor idea if as often happens we get 100 mph winds.

Are there alternative fixing methods which are unlikely to damage chimney stacks in high winds?

Reply to
Windmill
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Can you put it on the flat roof?

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rating-Roof-Mount

Advantage is no drilling of the communal parts.

Owain

Reply to
Owain

On Sunday 21 April 2013 11:43 Owain wrote in uk.d-i-y:

NonPenerating-Roof-Mount

Are those things safe on hot-felted roofs? I can see the weight causing it to sink into the felt on hot days.

Reply to
Tim Watts

In message , Tim Watts writes

I've fitted a couple of them recently and put about 1" thick rubber matting, stable flooring, beneath them. This spread the load on the roof material. The aerials I was fitting weighed a lot more than the average TV aerial too.

I also only paid just less than half the price asked in the above link, it would pay to shop around.

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Reply to
Bill

See

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There's a sand bed under the slabs to act as a gasket, make sure there are no pressure points. Bill

Reply to
Bill Wright

If the brickwork is strong it's OK. But spread the load widely like this:

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and not like this:
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The leverage on individual fixings caused by too small a footprint on the masonry is what causes the problem. Something like the first pic is OK, AS LONG AS the brickwork is sound. The test for the brickwork is to drill it with an aggressive hammer drill. If the bricks don't move or split it suggests the wall is OK.

Bill

Reply to
Bill Wright

Unfortunately that link doesn't work.

I would be extremely nervous - repeat *extremely* - about doing that. The whole flat section of the roof is the tarred arrangement usual for tenements here, it is regarded as a communal roof, any damage to such is known to cause leaks into/from top floor flat ceilings, and the repair bills when a roof reaches the end of its expected life is commonly

30,000 to 40,000 shared among all owners. (The dish is for a first floor flat on the wrong side of the building, i.e. not top floor and with no southern exposure.)

I wouldn't want to be the person demonstrably responsible for damage !

For the above reasons I hadn't even considered a roof mount, and was wondering if there was some way to securely attach a dish to the side of the chimney stack, maybe with some multiple bracket arrangement to provide more strength. TV aerials are often attached by a single bracket bolted into the brickwork, but that might not stand up to the stresses caused by a dish in high winds.

There might be room for some kind of contraption fastened below the angle bracket and cable for the existing dish, which belongs to someone else. Maybe a small angle bracket plus a long length of angle iron bolted to that and also into the wall halfway along the chimney stack, the whole thing being used to support a mast half way along.

Someone must have had to deal with this before.

Reply to
Windmill

I managed to find what I think was the item with the non-working link (maybe one of these pages which can only be reached from one particular other page - something to do with a 'Referer' field browsers send to servers IIRC).

They say that that mounting device uses four paving slabs to hold it down. Unless a mechanical engineer told me otherwise, I'd be afraid to use that on a recently and expensively renovated felt roof which rests on timbers which may be 100 years old. Especially as it's a communal roof; my name would be less than mud if there were problems.

But I saw on that site other mounts which are intended for large dishes and are stated to require mounting across several bricks. That gives me confidence that I could have a suitably large rectangular plate, sized to fit the particular location, made up and welded to steel tube for a mast.

Seems to me that it might be wise to have it bolted to several bricks above, below, and especially on each side.

Reply to
Windmill

That will be a good return job when the slabs move under vibration and the dish needs realigning.

Any low flying aircraft going past?

They should have used broadband and not bothered with a TV.

Reply to
dennis

Are you sure that spreads the load?

It looks like the top bracket will just transfer the reactive load to the second one down and the rest will not do much.

How stiff is the pole? Will it actually transfer the load between brackets?

Reply to
dennis

There is a large dish mounted on the side of a building near where I work. Its over a public footpath and is held up by what looks like 3" tube and a flat plate about 15" sq.

I always walk along the other side. The building is quite old and its rendered so there is no way the fitters can know the brickwork is sound enough for the fitting.

Reply to
dennis

What you're trying to say is that all the force from the wind is taken by the top two brackets, with the rest doing nothing. In fact that doesn't appear to be what happens. The mast is a scaffold tube, not a thin tube-wall aerial mast.

I've been doing installations like that for 40 years and I haven't had a failure yet.

Bill

Reply to
Bill Wright

But have you tried it with just two brackets and had a fail?

At least it looks good to the customer to go OTT.

Reply to
dennis

No, but I've seen plenty of instances where others have done just that. My website is full of them.

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More likely the housing association or landlord will complain about the unsightly brackets. And I like to be OTT if the alternative is to risk failure.

Bill

Reply to
Bill Wright

Um, you seem to have four brackets designed to resist a horizontal load but nothing designed to resist a vertical load.

I'm not saying that it's not strong enough but it seems an odd choice. Surely it would be better if the bottom bracket was designed to transfer vertical loads to the wall?

Tim

Reply to
Tim+

What do you mean, 'um', in that tone of voice?

Surprisingly there's absolutely no need for the bottom leg as used on 'spider' brackets. You could climb up those brackets like a ladder. In fact when the scaffolding is up I have done that many a time. The wall bolts are firm enough to resist the downward force. It is surprising I agree, but it's true. These brackets are made from very thick metal by the way! They aren't like ordinary TV aerial brackets. There doesn't have to be four brackets.

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If the mast was guyed vertical support would be essential though.

How about these wall brackets?

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The mast was very tall and guy wires weren't possible.

Bill

Reply to
Bill Wright

A beautiful bit of engineering, Bill.

Even if all four U-bolts fail the assembly wouldn't crash out into the street. :-)

Reply to
Frank Erskine

All thanks be to Ron Causer of Rossington Light Engineering.

Bill

Reply to
Bill Wright

The problem as I see it is that the top bracket will always take the full wind load and if you put extra brackets in they just act as a fulcrum allowing the wind load to have more effect on the top bracket. I would say its going to be more resistant to wind load if you just have the top and bottom bracket, at the same spacing, as the lever effect is less.

I could be wrong but without wind tunnel tests I will stick with what I think and it doesn't matter as I have never fitted an aerial mast, I leave it to the professionals with insurance.

BTW you may well have fitted one for me many years ago, it was someone named Wright who did it. Do you do stuff in the Midlands?

Reply to
dennis

Practical experience suggests the opposite. I understand what you mean, but when we do routine checks (we go to these systems for various reasons and will incorporate an aerial check now and then, especially when the aerial is over a footpath) we don't find evidence of excessive force at the top bracket. This evidence (often seen on other installations) would mainly be slight looseness at the wall bolts and U bolts, abrasion on the mast at the U bolts, etc). It appears that the four brackets together work with the mast to remain secure.

How about the real-life tests that we do, by installing these things?

When my information changes, I alter my conclusions. What do you do?

Yes, but I can't remember any domestic jobs.

Bill

Reply to
Bill Wright

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