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Housing - Renovation: The 'best' material for replacement window frames

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    • CommentAuthorgreenman
    • CommentTimeJul 26th 2010
     
    I have a two hundred year old cottage constructed from a mixture of cob, brick, and random stone, under a tile hung roof. Shortly after buying the house (about eight years ago) the windows were replaced with pressure treated softwood frames. I've just discovered that the sill to one of these windows already has rot in it, despite having been treated regularly (from new) with a good quality microporus waterproofing stain.

    I realise that hardwood frames are more durable (depending on the hardwood and conditions), but this has set me to wondering what is the best material for replacement windows in an older building, bearing in mind the often comflicting priorities of aesthetics, cost, durability, thermal insulation properties, sustainability, frequency, ease and cost of maintenance, and doubtless others I've missed out.

    I don't want to contemplate having to replace my windows again in the forseeable future, but if I do, then what's the answer please?
    • CommentAuthorbiffvernon
    • CommentTimeJul 27th 2010 edited
     
    Oak.

    It's the only material I ever use for making window frames. Should last a couple of centuries and then some. No need to treat with anything.

    (Chestnut if you live in Italy.)
    •  
      CommentAuthorTimber
    • CommentTimeJul 27th 2010
     
    Treated softwood should last more than just a few years.

    Perhaps the design of the window should be looked into rather than blaming the softwood?

    Timber
    • CommentAuthorjms452
    • CommentTimeJul 29th 2010
     
    You can insert boron gel and plugs into the effected timber (possibly from underneath where you won't see the hole).

    When the wood next gets damp this then begins to diffuse through the wood stopping the rot.

    Also quite environmentally benign.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 29th 2010
     
    Thet's gd news - does boron stay in there, if inserted from below? - as it's water soluble and is reckoned to leach out of exterior woodwork.
    • CommentAuthorjms452
    • CommentTimeJul 29th 2010
     
    I should say that I've never tried the boron approach but looked into it for a prexisting fence - I'm sure that it will leach everywhere over time. In low concentrations its actually aplant micronutrient so this isn't too concerning.

    When using it retrospectively you put in a fast acting paste and a plug of slower disolving stuff (then cap the hole).
    The paste is suppost to impregnate the wood initially, then the plug gradually disolves acting as a top up. I came across the technique in an old green builging book which went about borax incessentaly. Also saw accounts of councils using it telegraph poles where the creosote is wearing off...

    Its expensive so I gave up on the idea for the cheapish fence posts.
    • CommentAuthorgreenman
    • CommentTimeAug 18th 2010
     
    Thanks for your comments everyone - oak would certainly have been my first choice, but funds simply wouldn't stretch that far!

    Timber - I'd agree with you about the window design if it weren't for the fact that we had all the windows replaced at the same time, to the same design, and this is the only one to have suffered the problem (I hope!!).

    Perhaps I should buy some green oak now, and by the time it's had a chance to dry for ten years, I'll be able to make some replacement windows myself for a fraction of the cost (though of course it will probably all dry banana shaped )!:smile:
    • CommentAuthorsquowse
    • CommentTimeAug 18th 2010 edited
     
    cost of the wood is only about 25% max of the cost of a fitted and finished double glazed window. not worth skimping on the material as you have discovered.
    both pressure treating and microporous stains are attempts to make non durable wood durable and will only last a certain amount of time even if applied correctly, cut ends and hidden surfaces treated, which a lot of joiners don't bother with.
    something durable like oak is a good investment although i am wary of it's tendency to movement. but in experienced hands and seasoned to the right moisture content i am sure it is great. there are other durable woods available, some reclaimed.
    • CommentAuthorjoe90
    • CommentTimeAug 18th 2010
     
    I would love to make my own oak windows and have very good woodworking skills, what moisture level should the oak be dried too? and is there a good source of information on how to construct such windows (Biff, do you do masterclasses???) :bigsmile:
    •  
      CommentAuthorrogerwhit
    • CommentTimeAug 18th 2010
     
    For the uk about 15 to 20% moisture by weight should be fine for windows. There are lots of examples of window sections on line, but sections relate intimately to the hardware used, and in turn the exact form of the corner joints derives from the sections. I'd say that you need reasonable powers of 3D visualisation to succeed. Oak is good for windows I use it alot.
    • CommentAuthorjoe90
    • CommentTimeAug 18th 2010
     
    rogerwhit
    Thanks for your reply, I have very good 3D visualisation and perform lots of various joints in timber but have heard that there is a right and wrong way to build windows that last and I would welcome your help in a good source of information on this very subject.

    many thanks
    •  
      CommentAuthorrogerwhit
    • CommentTimeAug 18th 2010
     
    Sorry Joe I'm not aware of published sources. For durability moisture management is key, ie let it out or keep it out, which may mean protecting especially end grain (the most absorbent) before assembly when it becomes inaccessible. For all timbers, sapwood is BAD - yes, oak no better than the rest. Common commercial softwoods often include lots of sapwood by default.

    That's the wood, the other thing is to drain the rebates to keep the unit seals dry.
    • CommentAuthortony
    • CommentTimeAug 19th 2010
     
    ie all surfaces that could get wet or damp slope significantly down and out.

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