roof height and angles

[jow104]

My present garage height at wall plate (heighest) 94" =2.350m, and there are not any eaves present at the moment as per attached photograph. Therefore overhang can be acceptable to whatever measures that keep me under the 4 mtrs. total.

[duckman]

Hi Guys,

Promised drawing will appear soon. I'm having the @#$^&* time getting this @#$^&* scanner to work. Hrmmmph... :mad:

Not happy Jan!

Back soon..

[duckman]

Hi guys,

Still can't get my stupid scanner working so I've had to fire up an ancient CAD program which I haven't used for about 8 years. The drawing is consequently very basic.

The red triangle represents what you would get if you just used the formual already given eg
height = (tan(pitch) x 1/2 span)

When we superimpose a rafter(rafter is represented by the parallel green lines) of any size over this triangle, we see that to the figure obtained using the formula, we have to add the plumb cut at the pitching line and the thickness of a batten and possibly the roof cladding as well.

This is a lot easier to show someone out on site that it is to put into words.
If this isn't clear enough jow, get back to me and I'll elaborate.

HTH,

Mark.

[jow104]

Your efforts have been much appreciated and showing rafter as a separate green line marking makes things much clearer when coming to the final calculation.

How many hours would a professional roofer expect to allow for a roof of this size? Anyone got any ideas!

[duckman]

Hi jow,104

Your efforts have been much appreciated and showing rafter as a separate green line marking makes things much clearer when coming to the final calculation.

Any time.

How many hours would a professional roofer expect to allow for a roof of this size? Anyone got any ideas!

Depends.

Will you demolish the existing structure yourself? What is the law regarding the removal and disposal of asbestos in blighty? That could well be the most expensive part of this exercise.

Assuming the asbestos is removed 'by others', two chippys would demolish the existing roof and cut and pitch the new one, fascia, barge boards and roof battens in a day. That's what I'd allow. The only caveat I'd put on that estimate is that it assumes unobstructed access to the site eg that they don't have to negotiate a number of obstacles to get from where they cut the roof to the garage, that the timber is dropped outside your property and that the rubbish stays on-site and doesn't have to be carried down the block to a bin. Its only a straight gable after all.

Having said that, if you demolish the entire roof yourself, I'd still allow a full day. There's nothing one can really do with a spare hour or two at the end of the day.

HTH,

Mark.

[jackiew]

question - weight of asbestos roof is ( I would have thought ) quite low compared to the weight of a tiled roof ... is there anything that jow104 needs to inspect about the way the frame of the garage is constructed/his foundations before putting on the new roof? It would be a shame to reroof and then the whole thing collapse under the weight.

I ask this because when I bought a house which had had a slate roof converted to tiles the surveyor took special care inspecting the roof timbers and told me that tiles were much heavier than slate, which I think probably weighs about the same as asbestos sheet.

cheers, jackie

[Barry_White]

How about using the good old corrugated roofing e.g. a nice Colorbond then weight wouldn't be a problem or maybe it isn't available in the U.K.

[Ian007]

i know that our standards are/ may be different to the pommy one's but this is what we work on for load mass. I took this from the aus standards tried to scan it in but i couldnt read it so i just typed this little bit.
do they have to allow for extra loading in England for snow? I know that they do in some European country's

Jow104 you may need to find that out mate, cobber etc etc(spoken in an aussie accent)

10KG per M2 0.50mm steel sheet

20kg per m2 medium gauge steel sheet roofing,battens, 12mm softwood ceiling lining, sarking and lightweight insulation

60kg per m2 Terracotta or concrete tiles and battens

90kg per m2 Terracotta or concrete tiles,purlind,roofing and ceiling battens, 19mm hardwood ceiling lining, sarking and insulation

cheers Ian

Ps cant find anything re slate

[duckman]

question - weight of asbestos roof is ( I would have thought ) quite low compared to the weight of a tiled roof ... is there anything that jow104 needs to inspect about the way the frame of the garage is constructed/his foundations before putting on the new roof? It would be a shame to reroof and then the whole thing collapse under the weight.

Tiles on the roof of a free-standing garage Jackie? Geez, you have expensive tastes.
In Aust. specifically Victoria, there isn't much difference at all in either footings or wall framing in SINGLE STOREY construction between the structure needed to support a tin roof and a tiled roof.

I ask this because when I bought a house which had had a slate roof converted to tiles the surveyor took special care inspecting the roof timbers and told me that tiles were much heavier than slate, which I think probably weighs about the same as asbestos sheet.

I haven't had to deal with slate roofs for quite some time, so can't remember the relative loads. I'd have to look it up. Hang on a mo. Ian's done the 'looking up' for us.

Hope some of this helps.

Mark.

[duckman]

Ian,

would it not be true that if you had a longer rafter run then the finished height would be changed as the base width is changed?

are you saying that a building 6m wide with 30deg pitch would have the same finished building height as a building 5m wide with the same pitch?

Cheers Ian

In re-reading this thread I became aware that I didn't finish answering your question re the effect of adding an eave to the height of the roof.

I've tacked a 'tail' onto the rafter that I scribbled for jow. I think that the revised drawing will make it apparent that the overhang contributes nothing to the height of the roof.

HTH,

Mark.

[jackiew]

Tiles on the roof of a free-standing garage Jackie? Geez, you have expensive tastes.

I wouldn't put tiles on a garage roof ( unless, of course, I scored some for a bargain price ) because I'm a firm believer in look after the pennies and the pounds look after themselves" or "many a mickle maks a muckle" as they say in scotland but JOW104 mentioned he was planning on tiles.

There are garages and garages. I've owned a house in the uk where the lightweight timber and asbestos garage couldn't be used for cars because the timbers spanning the roof had "pit props" holding them up because they'd snapped. that's one garage I wouldn't be putting a tile roof on even if the tiles were free!!! And depending on who put the garage up the foundations might be negligible or non existent. :eek:

[duckman]

G'day Jackie,

There are garages and garages. I've owned a house in the uk where the lightweight timber and asbestos garage couldn't be used for cars because the timbers spanning the roof had "pit props" holding them up because they'd snapped.

Snapped? Yikes! That's one roof I would be demolishing from underneath.

that's one garage I wouldn't be putting a tile roof on even if the tiles were free!!! And depending on who put the garage up the foundations might be negligible or non existent. :eek:

Foundations are funny things, no really. By today's standards, many of the old wouldn't pass in a pink fit, but, most of the structures built on those foundations are still quite sound. That doesn't mean however, as you've observed, that those same foundations would be suitable for a substantially modified existing structure.

Here in Melbourne, in what we term 'the sandbelt', bayside suburbs where the soil is just sand, the foundations of a lot of the older homes are just a shallow trench, say 6 inches deep, into which large blue stone blocks were laid. These blocks are about 2 feet long and roughly 10 to 12 inches square, measured at the ends. Solid brick walls with terra cotta tiled roofs were built on top of them. Those houses are for the most part, still damn solid.

Hooroo..

Mark.

[jow104]

You lot have certainly of got me thinking. The asbestos roof has got to go in the near future. In the winter it condensates and frost forms underneath.
At the present time the two outside walls carrying existing weight are 4" thick concrete blocks with an 18" pillar in the middle and two corners. Front, no wall (lintels will be required but there is an 18 wide x4" thick block dividing). Back wall I suspect foundations are not up to scratch. I shall most probably have to dig down and have a look. The two outside walls which would I assume carry the roof weight I feel confident that foundations will be OK, and these walls look in very good condition.

[duckman]

You lot have certainly of got me thinking.

Fantastic!

<snip> Back wall I suspect foundations are not up to scratch. I shall most probably have to dig down and have a look. The two outside walls which would I assume carry the roof weight I feel confident that foundations will be OK, and these walls look in very good condition.

With a gable roof, only the side walls carry any roof load, so the back wall's footing is really neither here nor there. That might save some money. The front wall also doesn't carry any roof load, however, you do have concentrations of load because of the door opening and the weight of the door too. I don't know what type of garage door is most popular in England, but roller doors and panel doors can get a bit weighty if spanning a double opening.

Hooroo..

Mark.

[jow104]

I would prefer single doors. These are the doors used at the present time, but will most probably be replaced with new modern plastic variety.