Roof tiles and joists

Discussion in 'Builders' Talk' started by dappyduck, Feb 8, 2019.

  1. dappyduck

    dappyduck New Member

    Hi, I am planning to insulate the ceiling of our loft - ie - the roof below the tiles. However, we have a very old house and the builder has put lumps of cement between the joists and the tiles - presumably to ensure ventilation.There is no roofing felt - All there is are the tiles, and the joists, and the lumps of cement. However, the cement lumps are now so old that they are decomposing so that there are always lumps of old cement which have fallen on the floor of the loft, and the dust from the cement. Of course I'm presuming that I will need to remove whatever lumps of cement remain between the tiles and the joists, but am worried that then the tiles won't be supported - (presumably these lumps of cement also support the tiles so that they don't touch the joists.
    I would be extremely grateful if someone could tell me where to start with getting rid of the cement lumps - and what to replace them wich and how to replace them, if necessary.
    Many thanks!
  2. fostyrob

    fostyrob Active Member

    Pictures would be useful but I doubt it will be cement and I very much doubt it will be holding on the tiles (definitely tiles and not slates?). It is on the inside of the attic roof isn't it?

    They used to press lime mortar onto the back of and in between the sarking boards of horsehair and slate roofs prior to felt. Ventilation was simply through the gaps between slates and the boards.

    What nick is the roof in generally? Might be time for a new one? I suspect if you remove the "cement" you might get some water leakage but do not think your tiles will fall off.
  3. dappyduck

    dappyduck New Member

    Many thanks for your quick reply, fastyrob. Yes! I said 'cement' because I had no other way of describing the 'lumps'. Lime mortar sounds more like what I am seeing. I will get a photo but it might be tomorrow.
    If it is lime mortar - could/should I remove it - since it appears to be decomposing (the tiles are fine, we never have a problem with leaks.) We could not afford a new roof anyway, that is a lot the reason why I want to be careful with the one we have. After removing the mortar - would I then need to put in roofing felt?
    Thank you.
  4. dappyduck

    dappyduck New Member

    Apparently they are slates not tiles. Sorry.
  5. masterdiy

    masterdiy Active Member

    - would I then need to put in roofing felt?
    To put roofing felt on, first you need to remove the tiles. Felt, then new battens to hold the tiles.
    This would then create a warmer/better loft space.
  6. fostyrob

    fostyrob Active Member

    Trouble is that the roofing felt or these days a breathable membrane would be underneath your tiles or slates on the outside of the roof. You cannot retro-fit one without removing all the tiles/slates.

    I would certainly would not fix anything to the back of the roof as this will restrict ventilation and you could end up with rot.

    If it were me I would brush off the loose lime mortar or cover up anything you store in the loft.
  7. dappyduck

    dappyduck New Member

    Thank you. However, I could never remove the slates, That would, wouldn't it, mean the whole roof. I don't have the ability to do that, or the money to get someone else to.
    Is there an alternative? What i am wanting is to end up with a clear attic, with plasterboard on the ceiling, but I know that I have to keep the spaces between the joists ventilated, and would like to put some sort of insulation between the plasterboard and the slates.
  8. fostyrob

    fostyrob Active Member

    I assume this is for storage instead of to be a habitable room?

    If you do not have any leaks you could simply put up plasterboard at the moment whilst still leaving sufficient space for ventilation (50mm I think off the top of my head). If however you have an old slate roof (presumably with horsehair underneath- how much remains we don't know) with lime plaster on the back of the sarking a leak in the near future would be a distinct possibility.

    I would not insulate the roof but insulate the loft floor to keep the heat in the main body of the house.

    Ideally it would be a new roof but as you said this is not feasible.
    Last edited: Feb 8, 2019
    masterdiy likes this.
  9. masterdiy

    masterdiy Active Member

    Ditto above.
    Plasterboard would not last, waste of money.
    Do a good job with insulation on the loft floor. Then board. If you see damp patches then on the boarding, you know water is getting in.
  10. dappyduck

    dappyduck New Member

    Hi, fostyrob Thank you for your advice. I had hoped that it would be possible to make the loft a bit habitable. It is a very good size. And I am aware about not putting anything too heavy on the floor etc. However, after hearing from you that it would be best just to plasterboard - (I'm presuming i would need to fix extra batons on the joists to get them to 50mm if they aren't that wide?) - But all my plans for making it more habitable - ie, desk space - are disappearing like bubbles in the air!
  11. dappyduck

    dappyduck New Member

    Thank you too, for your reply, masterdly. - please see my recent message to fosty rob. Oh dear.But at least the roof doesn't leak at this point.
    masterdiy likes this.
  12. stuart44

    stuart44 Active Member
    Have a read through this.
  13. dappyduck

    dappyduck New Member

    Thank you, Stuart44. So its called 'torching'. It sounds a lot more complicated than the 'cement' that I thought it was to begin with. It will take a while - and lots of internet searches - to decide where to go from here! Thanks again.
  14. David Hatim

    David Hatim New Member

    Save up and put a new roof on
  15. dappyduck

    dappyduck New Member

    Thanks, David Hatim! Those words always fill me with laughter:D - and they would to anyone else in the same situation.:rolleyes: Save up? Save up? o_OWhen one has nothing left over to save??
    But I'm not complaining! Happy life - especially when one is able to learn new things - that roof has been puzzling me for years - and its great to now understand about torching and a lime and mortar and horsehair mix.
    Thank you so much to everyone.
  16. Powerelec

    Powerelec Member

    Old slate roof, I've had a few properties like this, leave well well allone don't mess with it, You're asking for trouble and you may end up having to have it re-roofed. Insulate the floor and leave it. Soon as you start knocking and banging on the rafters you may end up with leaks at some point. Ideally you need to get a new roof on if you want to use loft space.
  17. Richard AJ

    Richard AJ New Member

    Insulation between the ceiling binders will be the most suitable option. Given the roof slating itself is finished to the underside with torching, it's not as breathable as modern membranes. The rafters will be original and in addition to insulating between them causing damp to the reeds (or even lathe) and lime, you run the risk of iron fixings in any high level ceiling binders corroding. It's usually really difficult to add modern building materials to tradtional construction without inadvertantly reducing the life expectancy of structural elements. Lime mortar does degrade with age but it's worth remembering that all "non-hydraulic" lime mortars perform in a compreletly different way to modern portland cement based mortars. Non-hydraulic Lime mortar isn't as hard as modern mortar, its typically weaker and gets its strength from reacting with CO2 (turning back into limestone) in the atmosphere as opposed to water, which is how OPC (ordinary portland cement) and NHL (hydraulic lime) hardens. That's the main reason why the lime mortar is dusting off and "lumps" are breaking off. It's age related but will likely outlive you (unless tiles slip).

    However, there are other issues with what you're and others are proposing. Removal of more than 25% of roof covering will need building control approval, which leads to the potential for BC inadvertantly applying modern regulations, which means you'lll need to consider U values (R values), which require sufficient insulation to meet Part L1B. Then there's the age of the building and I'd start to think about its location and potential for it being in a conservation area or being an Article 4 building or even listed?

Share This Page