Re: DIY Loft Conversion Help

I am looking to do a loft conversion in my house, but the roof is

> supported with trussed rafters. I am looking for some advice on how to > create an alternative support for the roof so i can take take these > out and create some usable space. I have taken a few pictures and made > a drawing of the roof. I can supply measurements of the timber pieces. >

Unfortunately Brano, in the late '60's / early '70's penny-pinching builders started adopting the "fink truss" roof, found in your house. This was invented in the 1940's during the War Effort to save decent timber for building aircraft etc. by reducing the strength (read size) of timber for roofing. There was no consideratioin given to the likelihood of anyone wanting to use the space in the loft, and other aspects of houses built this way are affected - the ceiling joists are designed only to support the plaster and loft insulation, for instance (water tanks often have to be sat on specially constructed platforms of "proper sturdy wood" to pass the loads to the walls), the upper wall structure is designed to take smaller dead loads as the fink truss is lighter by far than the traditional "cut roof" joists anad purlins. A by-product of this change is that roof pitches decreased from around 45 degrees to between 20 and 30 degrees, with a corresponding loss of loft height - to make an usable room one needs a height of at least 7' over most of the floor.

To even consider a loft conversion, you *need* the services of a structural engineer as the fink truss is an unitary structure - all the elements are required to share the loadings - and removing one element will quite likely mean that other elements are taken beyond their permitted loads, with the risk of collapse... it'll need a complete new roof strucure of full-sized timber, probaly steelwork as (for example) the spans betwen supports for the roof will exceed the building regulation defined maximum for unsupported purlins . While designing the new roof structure it''s likely that the architect / structural engineer will consider that the wall structure isn't adequate for the new loadings (particularly if there are stud-and-plaster internal walls or timber-frame external walls, requiring additional structural work down to foundation level... you'll need to install new floor joists alongside the existing ceiling joists (which can't be removed in advance, as they tie the building walls together and prevent the outward roof load toppling them), probably 8" by 2" minimum, raising the current "floor" level by 4" or so. The increase in "floor" height will reduce headroom, meaning you'l need to either raise the ridge line or install dormer windows... it goes on and on.

G/f and I are in the final stages of buying a house together, with the possibility (or probability) of converting the loft firmly in mind - we eliminated anything built since 1960 - 1970 for just these reasons!

My considered advice is: . . . Move house [1]. It'll be cheaper and less disruptive.

Dave H. (The engineer formerly known as Homeless)

[1] to a nice trad house made of bricks with a nice trad roof made of 8x2" and bigger timbers
Reply to
Dave H.
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That's "summer" these days isn't it ;-)

Cheers Dan.

Reply to
Dan delaMare-Lyon

Firstly Thanks everyone for your posts.

Just to answer few queries here:

I have contacted the council and they have basically say that I can do either an application with submiting the plans or without submiting the plans just a notice of building or something like that both are going to cost me 180 GBP

Dave H. :

The adjoining part of the house I believe that there is a load bearing wall between my house and neighbours house and that the big big timber structures are on both sides of it so I will only be working with mine ones not the neighbours...

Baz :

no worries just looked to me like you work for them... ;o)

Brian G :

Flooring Ok could you tell me what flooring i need then if 4 x 2 is not enough I believe that the flooring timer piecies are on a load bearing wall on both sides...

I am not going to be doing this myself I am going to get my dad to do this... but I am looking for ideas on how to do it from people who did it themselves...

You say I need to conctact professional and then you also say that you are qualified to take it from you. I will take it from you just give me some advice rather than talk about speaking to a professional and putting lives at risk...

Calculations - The whole topic of calculations is for sure one school lesson that is no longer than 3 hours so why make such a big deal out of it there must be a mathematical solution to it could you tell me this rather than anything else?

Mortgage - this bit was really interesting i didn't know this thanks I will contact them and see what they need.

BTW Anyone knows any structural engineer in Belfast area?

John Rumm :

Your site looks definetly good just like the thing I am looking for. But I havent find anything about supporting the roof there is this cos your property had a proper roof before you started?

they only told me that I have to apply for a building notice (180 GBP) and I can start doing the conversion. I am intending to do that.

You say you know how to calc this could you tell me how?

Exactly why i have posted here...

Hugo Nebula :

Hi I am not sure what you mean by monopitch. But as you are looking at the picture that I drawn both on the left and on the right they are load-bearing walls. On the top it is supported on the big trussers that are on a LBW.

The council (building regulations) said i do not have to submit plans that I can just submit a building notice and start the work.

Thanks for everyones response !!!

I will keep posting here about the progress. Please post back with any more info.. THX

Reply to
Brano

The cheapest method is probably to remove the entire roof and build it again properly. Trussed systems are simply unsuited to conversion. They are computer designed to save every cm of wood and only resist the loads used in design, which did not include several people and furniture.

Modification of the existing would be fiddly, and, in all probability, more expensive because of the labour cost.

An additional advantage of entirely reroofing is that the roof covering gets relaid and you get to install breathable membrane felt which lets you install more effective insulation.

Christian.

Reply to
Christian McArdle

What is the clear span of the timbers?

Assuming no heavy fixed dead loads (i.e. just normal flooring, no partition walls). 600mm spacing between joists.

4x2 (50x97) = 1.58m 5x2 (50x122) = 2.37m 6x2 (50x147) = 2.86m 7x2 (50x170) = 3.29m 8x2 (50x195) = 3.73m 9x2 (50x220) = 4.17m

You get a bit extra span by spacing joists more closely. You get a bit less if you have some heavy dead load.

Christian.

Reply to
Christian McArdle

I dont know whether in such situations you could stretch to another 2' of wall height added on, but if you can that will much increase the usable space up there.

NT

Reply to
meow2222

On 3 Jul 2006 02:23:26 -0700, a particular chimpanzee named "Brano" randomly hit the keyboard and produced:

Then either: a) you haven't been completely honest with them as to the extent of the work you're proposing; b) they have misinterpreted what you're proposing to do; or c) as a Council tax payer you should be asking why your Council is only charging half what the rest of the country is and losing money on loft conversions hand-over-fist.

...for free?

Legally, yes you can. However, practically speaking unless you can answer the following questions, I would suggest you need to work from plans:

  1. Do you have an enclosed escape route and an alternative exit from the loft, or will you have a completely protected route with 30 minutes fire resistance?
  2. What size will your rafters, floor joists and trimmers, etc. be?
  3. Will you be removing the ties at wallplate level, and if so how will you prevent lateral movement?
  4. What insulation will you be using between and under your rafters, and how are you going to maintain cross ventilation?
  5. What wattage will your radiators be?
  6. How many energy-efficient light fittings will you be providing?

With a Building Notice, there's a presumption that you know the answers to these questions (and more) and that you have a modicum of ability in what is needed to comply with the Building Regulations. If not, then you really should take professional advice before starting. It's like learning to drive without an instructor by reading the car's handbook.

Oh, BTW, one of the questions is not covered by the Building Regulations. See if you can spot which one.

I'll wait to hear on the news, "man dies as roof collapses".

Reply to
Hugo Nebula

NO, its between the properties and shared, it's a PARTY WALL and you need to comply with the Party Wall Act - you'll need a legal agreement from your neighbours to do anything that impinges on the wall or the attached structure - please believe me, I have to get agreement from neighbours in order to convert my loft, as despite the wall between properties being the demarcation, it's a party wall because we both have it as our boundary.

Dave H, (The engineer formerly known as Homeless)

Reply to
Dave H.

"Dave H." to comply with the Party Wall Act - you'll need a legal agreement from

I think we're in new territory here in this group regarding Northern Ireland. Hate to give any credence to emissions from two shag's department, the Party Wall Act probably makes sense, but does it apply in Northern Ireland?

Jim A

Reply to
Jim Alexander

Jim Alexander :

thanks a lot those booklets look very useful.

Christian McArdle :

I will get the span measurements tonight...

snipped-for-privacy@care2.com :

;o) hehe

Hugo Nebula :

Well I double checked that is what they charge for it it doesnt matter what type of work it is that is the charge for the building notice.

Well if you have enough time to read google groups surely you have enough time to do it for me? You wouldn't want money for it would you? Money only destroys character believe me...

I am aware of these questions and seen them several times before:

  1. yes window, 30min fire res is the insulation and floorboards and firedoor
  2. thats what i am looking to find out here
  3. no as I am looking to rebuild the roof support from inside rafter by rafter.
  4. the yellow stuff from B&Q not sure what you call it. Ventilation never heard of that pls explain.
  5. I am looking to put a normal radiator there not an electric one...
  6. what is this do do with anything? Probably just one at the top as it would be a smallish room.

It's got to be the one about lights or radiators...

You seem like a very optimistic guy I can see that you will achieve a lot in your life.

Dave H.:

Actually there will be nothing touching the neighbours wall just stuff attached to MY wooden construction on MY side of MY house behind this there is a wall that I would not touch. And anyways there is noone living there and i belive its going to be rented out by someone welthy who bought it on a BUY TO LET mortgage.

Guys THANKS for all your quotes again...

I have a couple of new questions too:

What would be the difference if I only want to clasify this conversion as a roof storage?

Does anyone know more about what needs to be done about the mortgage company and loft conversion as the house is mortgaged?

THANKS everyone

Reply to
Brano

I presume you are aware of the specific requirements for escape windows.

You could be in trouble here. One of the fundamental issues with loft conversions is deciding on the insulation and ventilation requirements. You could write a book about it. I doubt that most B&Qs could supply you with any of the sensible competing materials. If you want to maximise space and headroom, these days you basically have a choice of Kingspan/Celotex type rigid boards between and under or Tri-iso Super X, which some people think doesn't work.

If you have existing sarking to the roof, then you must have a 50mm gap between the insulation and the sarking and this must be ventilated to the soffit below and the ridge at the top.

Normal radiators are also specified in watts.

There's a silly law requiring you to install a ridiculous expensive and ugly fitting that will take up landfill space approximately 15 seconds after the BCO has left.

You would be committing a criminal offence if you tried to pass this off as roof storage.

Personally, I would tell the insurance company, but the mortgage company could wait. They're not going to sue you if you add additional room (unless you c*ck it up badly and don't go through building and/or planning regs).

Christian.

Reply to
Christian McArdle

Actually, the Party Wall Act means you don't need permission or agreement from your neighbour. It gives you the entitlement to modify, strengthen repair or use it. The main thing it gives your neighbour is the right to be informed of the work and the right to appoint a surveyor at your expense to ensure that the works are done safely and compensation for damage is paid. They can't refuse you permission. If they try, the courts can (and will) issue injunctions against them interfering with the work.

Christian.

Reply to
Christian McArdle

To which your roof structure attaches, I presume, or will it be suspended on skyhooks? If any of the roof timbers attach to the party wall, you are liable if anything you do affects the adjoining building. I have to make a PWA agreement with my next-door neighbours because I want to remove the purlins in a trad' cut roof after installing new steelwork to take the roof loadings, despite the fact that they don't extend into the adjoining property - they attach to the party wall, so they affect the neighbours' property.

. And anyways there is noone

Who can probably afford an expensive civil lawyer to sue you into bankruptcy if anything goes wrong (as can his mortgage lender), or if all goes well and the PWA or similar applies, make you reinstate or modify the structure to his satisfaction.

It's not really a question of how you classify it, it's down to the local authority building control officer, if he thinks it's an habitable room, it has to meet the regulations.

The mortgage company will want to see your architect's or structural engineer's plans and the building control notice and will want an indemnity in case you wreck their property (having a charge over it, they have as much of an interest in the building's remaining upright and sound as you do).

Reply to
Dave H.

As it happes they were not in the slightest bit interested in my conversion. I phoned them to query the bit in the policy doc that said "you must not make any changes to the property without our agreement" etc. and it was a case of "yeah whatever!".

Reply to
John Rumm

Sounds cheap, but perhaps things are different in NI. Cost me about double that all in IIRC.

The table Christain gave is a start, but that does assume "normal" floor loads. If you end up with partition walls etc on those floors then needless to say that makes things somewhat different.

Alas it is not that simple. On my web site I have posted links to the software that I and my architect used to do the calcs. Given the right information it makes doing the sums very simple.

Understanding what information to feed into the software however is a different question. The danger of the software, is that it will simply help you design something wrongly much more quickly. The values you need to feed in, will in turn depend on the existing construction, and how you plan to modify it.

Worth doing to cover your arse if nothing else. You may find they are not too fussed. (although when I phoned them and said "I am doing a loft conversion" they may not have interpreted that "I" quite as literally as I meant it! ;-)

Yup mine was a traditional joinery roof so there was not much extra to do to make it suitable. I did take out a purlin and replace it with a dwarf wall, and I also took out the balancing rear section of roof. This would normally require a beam along the ridge to carry (the now unbalanced) load of the front roof, but since I was having a dividing wall across the middle of the space, this was made load bearing and the dormer ceiling joists take the load of the front roof in cantilever.

With 20/20 hindsight I may have also de-tiled the whole roof and re done all the felt and battening. That way I could have used a breathable sarking that would have allowed use of more insulation, and also saved titting about with ridge and soffit ventilation.

Assuming things are the same where you are, you have the choice of going the building notice route, or the full plans submission route. The former is good if you know what you are doing and can work out the detail on the fly. The latter is better if you would feel happier with a general "ok" to the major aspects of the work in advance. The full plans submission can save you some nasty (i.e. expensive) surprises later!

You need some source data: things like loadings, and joist spans, and how the joists will share loads (if at all). Some will come from your plans (which you need to draw or get drawn)[1], some can come from an architectural data source book (again see links on my web site).

From those you have something you can do some calcs with, and there is software available that will automate much of the work for you.

[1] Even if just using a building notice, don't be tempted to carry out this sort of job without detailed drawings of what you are doing.

I think he is referring to your drawing of the truss structure - you have only shown one side of the truss - i.e. it only slopes only one way and does not have a pointy bit in the middle!

Reply to
John Rumm

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