New pitched roof

Discussion in 'Carpenters' Talk' started by Dannyj84, Jan 15, 2020.

  1. Dannyj84

    Dannyj84 New Member

    Hi, sorry if this is in the wrong forum. I can't see a specific roofers one.

    We have an old garage pitched roof 22 degree pitch. It currently has 3x2 rafters and the roof is a corrugated metal type thing.

    It currently has 7x2 ceiling joists which are 2.8m long. The rafter are about 3.1m long.

    We want to remove the joists and open up the roof as the current ceiling is only about 2.2m high. We also want to replace the current roof with lightweight tiles.

    So our plan is to remove the current roof completely. Put in some new rafters 6x2 c16 timber. Spaced about 500mm apart. Then insulate between the rafters and plasterboard.

    Currently the roof has some kind of chipboard above the rafters so not sure what kind of ventilation there is but I've read you need ventilation in the roof space. So packing the space in between the rafters doesn't seem like a useable option?

    Can any one advise the best way to go about removing the joists and just having rafters and leaving a diaganol ceiling.

    Thanks
     
  2. Montythecarpenter

    Montythecarpenter New Member

    Is it gable to gable or hipped?

    You're trying to make a vaulted ceiling BTW.
     
    Last edited: Jan 15, 2020
  3. Abrickie

    Abrickie Screwfix Select

    500mm spacing, that’s a lot of plasterboard waste
     
  4. Jord86

    Jord86 Screwfix Select


    No offence but I’d employ a carpenter to at least build the new roof for you, you come across as out of your depth. You’d need overfascia vents as a minimum, or a vented soffit, with a dry ridge system so the air travels up through the rafters to the ridge. 400 or 600 centres, 500 is a non divisible measurement, and pointless. Strip off the old roof and cut and fit the insulation and plasterboard later on but I’d leave the construction to someone who does it for a living.
     
    Dannyj84 likes this.
  5. Dannyj84

    Dannyj84 New Member

    Thanks for your advice. I think you are probably right. I have spoken to a few local companies. The next question I have is, my local planning site says that I need to inform building control with a building notice for changing a roof. There is a 200 fee but none of the companies I have spoken to say that I need to inform building control. 2 I have spoken to have over 30 years of experience and say they have never heard of this. (They aren't on the govts competent person scheme either)

    So to change the roof does the council building team need to be involved? I don't want to come to sell the house 10 years on and have issues.

    Many thanks
     
  6. rogerk101

    rogerk101 Screwfix Select

    I have just changed my flat roof garage to create a two storey granny flat. I had to change the roof anyway as it was rotten, but I chose to replace it with a gambrel roof (two pitched roof with the first pitch at 65 degrees and the second at 35 degrees). This made a huge difference in the amount of usable space upstairs, so was well worth the additional hassle. I covered the roof with Tapco slate tiles, made from recycled plastic. They look really authentic ... far better than the composite slates that some people use to imitate real slates. They weigh 11kg per square metre, so about 20% of the weight of the concrete tiles I have on my main house.
    I did not inform the council so did it without planning permission. Unless you are on bad terms with a neighbour or you have a busy body in your street, no one is ever going to bring up the fact that you have changed your roof.
    According to a friend of mine who is a retired building control officer, if no one has objected about your change of roof for 4 years, then the council just has to accept it as the new roof. In my case, when the time comes to turning it into a granny flat, I will certainly have to apply for a change of use of the building - changing from workshop/garage to habitable accommodation.
     
    Jord86 likes this.
  7. Dannyj84

    Dannyj84 New Member


    Thanks, what span is the roof? And what rafter size did you use? Have you kept the roof open? Or does it have ceiling joists? Our current roof seems to be an odd way round 3x2 rafters and 7x2 ceiling joist... 3m span for the rafter 2.8m for the ceiling

    Danny
     
  8. Montythecarpenter

    Montythecarpenter New Member

    You cannot just bang rafters up of the same size as somebody else mate, you need a properly designed roof.
     
  9. Montythecarpenter

    Montythecarpenter New Member

    You can put 20x2 rafters on but without a proper design it will fall down. You are going to need a steel ridge beam if it's gable to gable. A hipped roof... Even more difficult. You can't do this as a DIY project, you need a professional to design it
     
  10. Abrickie

    Abrickie Screwfix Select

    Lol, you just know OP wants someone to give him the pitch, sizes and if you happen to be passing by with your tools :)
     
  11. Montythecarpenter

    Montythecarpenter New Member

    This could be dangerous if he goes ahead
     
  12. Dannyj84

    Dannyj84 New Member

    Tbh if the roof has stayed up in its current state for 25+ years there must be a fair bit of leeway the ledger board on the house wall is only 2x2 half the 7x2 ceiling joists have been cut out to allow access to store stuff I presume. Pretty much most things that I could do to it would be an improvement

    But anyway I've taken advice on here to get someone else in to do the woodwork. I'll just add the membrane battens and tiles
     
    Montythecarpenter likes this.
  13. Montythecarpenter

    Montythecarpenter New Member

    Sorry mate, only being blunt because your and your families safety is priority. This needs to be calculated by a structural engineer and signed off by local authority through building regs.
     
  14. Dannyj84

    Dannyj84 New Member

    This is why I queried the roofer saying they don't need building control involved. Also the planning website states that a roofer who has a competent person registration can do it without building control. I looked on the registration page and it literally asks for no qualification or evidence you can do the job... More interested in you paying the registration and yearly fees. But that's life eh.

    The local planning site also gives max spans for rafter sizes... As an example for a 6x2 rafter at 400mm intervals max span is about 3.23m. surely this has to be accurate and assume a heavy tile is used.
     
  15. Montythecarpenter

    Montythecarpenter New Member

    That's only true if adequately sized joists are used mate. Because you want to do a vaulted ceiling you need something to stop the top from dropping and the bottoms from spreading.. ie a steel ridge beam. But you need to know what size steel can take the weight (tiles and wind and snow which depends on location). I wouldn't mess about with this mate even as a professional, get the calcs and it'll breeze through inspection and most importantly will be safe
     
  16. Severntrent

    Severntrent Screwfix Select

    can't quite understand the existing layout, is it a lean to type of garage or one with a shed type roof? If its a lean to type the above, re spreading and dropping, does not apply
     
    Montythecarpenter likes this.
  17. Montythecarpenter

    Montythecarpenter New Member

    Ah true
     
  18. Dannyj84

    Dannyj84 New Member

    So the main house as normal.... Then a single story building attached to the left hand side of the house. Single sloped roof sloping upwards from the outer wall to the main house. Extension is only single brick construction no inner block. So it's been studded out with insulation and plasterboard.

    Building dimension are 2800 X 5600 roof slope is 22 degrees.

    Roof is corrugated metal type material and currently has 3x2 rafters that are around 3200 fixed to a ledger board that's 2x2 bolted to the main house. It then has some 7x2 ceiling joists sat on the outer wall spaced about 400mm apart and then another ledger bolted to the house wall and this has little notches cut out of it which the ceiling joist sit in. The rafter just sit on top of these joists when they meet at the external wall.

    That probably doesn't make it any clearer but that's how I'd explain it and why I'm a pharmacist and not a tradesman

    Thanks
     
  19. rogerk101

    rogerk101 Screwfix Select

    4m
    150mm, but that was not for structural reasons ... it was so that I could fit 130mm of insulation between the rafters.
    Yes, it's a fully vaulted ceiling, right up to the ridge.
    No ceiling joists, just a few collars tying the purlins together. These are well above head height so don't get in the way of any living. They're spaced every 1200mm.
     
  20. Montythecarpenter

    Montythecarpenter New Member

    Oh so rafters supported at the bottom on 4x3 wall plate and at the top on a pole plate. Not so bad building inspector will probably just tell you pole plate size that he's happy with and you can work rafter sizes from rafter sizing tables.
     

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