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Loft insulation project

Peckham Power are developing a community loft insulation project.  Please do join in the discussion below.

Originally submitted by Jack on Mon, 19/04/2010 - 1:46pm.

Last update on Mon, 26/04/2010 - 3:11pm.

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#1

Submitted by Jack on Mon, 19/04/2010 - 2:48pm.

Technical Challenges and Possible Solutions

This is a draft document, that I'll keep updating - this is co-written with Clyde and includes quotes from the Green Building Forum.  Please don't see this as Peckham Power's "recommended practice".  This is just us planning out loud.  Feel free to join the conversation.

Maintaining Ventilation

The wood structure of our old Victorian houses has remained relatively healthy over the past 100+ years largely because it's so draughty in Victorian lofts, plus the loft receives some warmth from the rooms below.  (The wood inevitably acquires moisture from a variety of sources; so the wood needs to breath to allow that moisture to escape faster than it enters the wood.  Damp wood is an attractive medium for many organisms, including fungi and wood worms).
 
Maintaining ventilation is relatively easy.  Firstly the ventilation gap built into the eaves needs to be maintained and there are simple, cheap products which can be installed to ensure the insulation doesn't block the eaves (e.g. eaves trays).  Additionally, vents can be installed in the roof tiles.
 
Clyde:
There are indeed good products available to ensure eaves ventilation can be maintained in new build conditions but I am not sure these will always be easy to apply in old 19century buildings. I am concerned that this issue may not seem very important now but in the long term  (10-20 years say) may accelerate rates of condensation and wood rot.
It's surprising how much ventilation you need. The general recommendation is for ventilation in both eaves so that air flows in one, across the loft just above the insulation and out the other side. The recommended area of the vents is around 10-25,000 square mm per meter. That's equivalent to a 10-25mm wide slot the whole length of the eaves...
...
Insulation at joist level: Vents at the eaves. Air goes in one side, across the loft just above the insulation and out the other.
Insulation at rafter level: Vents at the eaves and ridge. Air goes in at the eaves, up the 50mm cavity between insulation and membrane and out the ridge. If there is a dormer window or similar that blocks this cavity then there might be a case for a vent above and below the obstruction.
To quote brig001 on GBF:
Not sure if you are looking at eaves/soffit vents, but if you do, watch out for putting them above bathroom extractor fans. Steam from the bathroom was blowing back into our eaves vent causing condensation in the loft.
Brian.
 
I probably don't have sufficient eaves ventilation in this picture:
 

Access

Easy access to loft spaces may be the exception rather than the rule.  Some people might not have ladders.  Once you get up there, can you get to every single part of it?  Is it lit?  How easy is it to move around (you often have to tread carefully from joist to joist).  We need to survey.
 
Lofts are often too cramped to allow more than a couple of people (at most) to work inside the loft at once.
 
Lifting large items like bundles of insulation and wood up through the hatch is often tricky, requiring at least two people.
 
 
 
 

Cabling and lights

Cables need to go above insulation so they don't overheat.  Down lights need to be boxed over so the hot lamps don't touch the insulation; care needs to be taken not to introduce draughts.  I presume any pipework also needs to be under the insulation.
 

Water storage tanks and pipework

Important to note that these should be appropriately insulated with the roof insulation omitted directly
underneath.  In the longer term of course such storage tanks should become increasingly redundant.
 

Danger and discomfort to installers

Many lofts are dirty, dangerous, stuffy places which become unbearably hot in summer and very cold in winter.  It's very easy to put a foot through the ceiling (plasterboard is surprisingly weak stuff, it will break even if you put a fraction of your weight onto a free span of plasterboard).  They're dusty and there could well be dead rodents knocking around.
 
 I would definitely recommend you have a health and safety check list to give out and a generic risk assessment as it will educate and point out small hazards that people may not consider...
 
things like appropriate protective wear - gloves, dust mask and safety glasses. Ladder safety, ceiling joist awareness etc
Pipes and cables also create a trip hazard (and tripping over in a loft could easily send you through the ceiling).

Many houses round here have 3" deep joists which could be insufficient to support even a single person, see below:
 
"I would be careful doing anything up there if the joists are only 3" deep (even getting up there to inspect it). One large knot in a long span and you could go through the ceiling.
 
If the joists a bit deeper say 6" (again it deends on the span) for light storage you can form a platform by putting new battens at right angles to the existing ones. These need not be full length. Putting new insulation at right angles to the existing insulation is also a good trick. Ideally the platform would be high enough such that loft ventilation can go underneath.
 
If you need to upgrade 3" joists find out if there is a central spine/supporting wall. If there is then you might be able to get new half span joists in. These should be raised up about 0.5-1"  so they do not rest on the plasterboard. That way if they bend under load they don't crack the existing ceilings.
 
For difficult cases I believe there are telescopic aluminium joist systems but they are probably quite expensive."
The bedroom ceiling of a local home collapsed a few years ago (luckily they were out when it happened) so the structural stability of old joists is a very real problem.  People could be seriously hurt or even killed if we get this wrong.
 
 
 
 

"Doing it by the book"

 
the reason I asked about whose roof is that would change my perspective on things. If you're doing it for yourself you can maybe cut a few corners, keep an eye on things and hope for the best. But if you're going round doing work to other people's roofs, then I for one would want to do things by the book. No hoping that it's an old roof and so might be draughty enough already to not require dedicated vents. 
 
That might complicate things considerably, but it avoids a lot of risks.
I (Jack) tend to agree.  There are some serious risks to consider when insulating lofts, both to individuals and to the structural integrity of the buildings.  We need to do this by the book and step up our insurance, written codes of practice etc to a whole new level.
 

Building regulations

Building regs require you to make a building control application and upgrade insulation to specific standards if you are upgrading more than 25% of the area of what you have.
 
New Part L regs are due to be introduced some time soon.  We should check what u-value they require for roofs to make sure we comply with the new regs.
 

Fire

When we come up with a plan, we should probably discuss it with the local fire department or a fire inspector to make so it's OK from a fire perspective.


Types of loft

lofts come in many shapes and sizes. Frequently there are gables, bay roofs and just totally inaccessible spaces to contend with. There is also the question of those roof timbers such as struts, binders and purlins which always seem to appear in the most inconvenient places and which add to the difficulties of proper continuous insulation.
 

Loft hatch

The loft hatch needs to be insulated and draught-proofed.  This is not only to minimise heat loss but also to minimise the flow of water vapour into the loft.
 
 
  

Other considerations

  • Leaky roofs need to be fixed and, ideally, left to dry out before insulation is installed
  • Beware asbestos insulation (A discussion on ScrewFix.com seems to suggest it's unlikely but not impossible to find asbestos used as a loft insulation.  A discussion on GBF also says it's very unlikely to find it used between the joists in place of glass fibre but it may be used in paint / tiles / boarding (used as a fire retardant))
 

Grants

Need to point people towards any grants they are eligible for.
 

Distilling all the options into a flow chart?

The general message is: the layout, structure and usage of lofts is bound to vary considerably.  We almost certainly can't offer a "one size fits all" solution.  Indeed, each case may need some quite careful consideration by a structural engineer.  Or perhaps we could produce a flow chart to cover 90% of eventualities (perhaps wikify the flow-chart, perhaps on EnviroWiki.org.uk, perhaps using a shared Google Docs Drawing) which would be checked by an engineer?
 

The insulation options

 
4533759649_52dcc77ac1_o.jpg
 

1) Just put glass wool insulation over the joists

 
making a total insulation thickness of 270mm.
 
Advantages:
  • Cheap
  • Relatively quick & easy
  • Standard procedure; people have done this before!
Disadvantages:
  • Can't put anything on top of the insulation
  • Can't walk on the insulation (because you can't see where the joists are)
If the loft needs to be used for storage then:
  • Store junk on shelves supported only by the rafters (i.e. shelves which don't touch the floor, leaving the floor clear) (this has the added advantage of minimising the weight on the skinny joists; a neighbour's ceiling joists collapsed a few years ago)
    • It probably wound't be necessary to empty the loft to install the shelves.  i.e. the workflow would be:
      • install shelves
      • put junk on shelves
      • install insulation
  • Make a small walkable part of the loft so you can access the shelves (e.g. by using rigid foam board insulation covered with ply for the walkway or by raising the hight of the joists for the walkway)

Warnings:

  • If they joists are only 3" deep they may collapse while climbing on them to install insulation
  • Maintain eaves ventilation
  • Wear protective clothing

2) Install rigid foam insulation over the joists and then lay a thin layer or ply over the foam.

If you have 80mm (3") of existing mineral wool insulation between the joists then you need another 100mm of rigid foam insulation to achieve the insulation performance required by building regs).  Ply / hardboard / OSB needs to be installed beneath and above rigid foam to spread the load (excellent discussion on Green Building Forum) "plywood deck fixed to existing joists, rigid insulation to top with points taped & fully floating OSB floor to top".

 
Advantages:
  • The finished surface is able to take load (i.e. a person can walk on the surface and put their junk on top)
  • Could be installed in stages, as suggested by Yvonne.  e.g. you clear the left side of the loft and then you install insulation on the left.  Then you move all your junk onto the insulated left side while you insulate the right side.
Disadvantages
  • Rigid foam is slightly more expensive than glass wool.  A 2.4m x 1.2m of 100mm-thick foam board is £25 new, probably cheaper from B-stock suppliers.
  • Definite danger than condensation will get trapped under the ply.  Before rolling this out, we should really test it on a few houses for a year or two to make sure there aren't any condensation problems.
    • (What's the problem with condensation?  Warm, moist air drifts up from the living space into the loft.  The water vapour condenses on any sufficiently cold surfaces.  The ply above the insulation will be cold and hence could attract condensation during winter.  This condensation could drip into the joists and cause damp issues.  I have evidence from my own loft which suggests condensation could be an issue with this strategy)
    • The condensation issue could be mitigated somewhat by replacing the ply with a more breathable product and/or raising the ply above the insulation to leave a ventilated gap under the ply
    • I've asked for comments on the Green Building Forum
    • I know Eileen has floor boards installed over the 80mm of insulation in her loft floor.  In winter, I could ask Eileen if I could pull up one of her floor boards to see if there's any condensation under it.

Case-studies

3) Remove any existing glass wool and install just 150mm of rigid foam between the joists

 
This doesn't have many benefits unless the joists are more than 150mm in depth (and most Victorian joists are under 100mm in depth).  You need 150mm of foam to satisfy building regs. If you have 100mm joists then the 150mm foam will stick out above the joists and if you put load on the foam then it will cause the plasterboard beneath the foam to fail and the ceiling will have a big hole in it.
 

4) Add new joists running perpendicular to the existing joists, ideally supported at the ends so you don't add any weight to the old joists, then fill both the old and the new joists with glass wool insulation

 
Advantages:
  • Done right, you'd have a strong, stable floor to walk on in the loft
Disadvantages:
  • The new wood alone would probably cost in the region of £200
  • It may not be possible to get the wood up into the loft through the hatch in the lengths required (the roof structure would have been constructed prior to the tiles being installed)
  • Wood is heavy!
  • Quite labour-intensive to install

5) Insulate between the rafters

Insulate the space beneath the roof tiles rather than the loft's floor.  Leave a 50mm gap between the top of the insulation and the roof covering.  Ventilate this 50mm gap to the outside ("Vents at the eaves and ridge. Air goes in at the eaves, up the 50mm cavity between insulation and membrane and out the ridge. If there is a dormer window or similar that blocks this cavity then there might be a case for a vent above and below the obstruction.") Ensure the loft space is no longer too draughty (the loft space needs to stay warm; excessive draughts will remove that warmth).
 
Advantages:
  • Doesn't add any weight to the joists
  • You don't have to move any of the junk from the floor (although it might be necessary to move the junk around so you have a stable platform to stand on whilst insulating the loft)
  • Keeps the loft space warm in winter and cool in summer
  • The really quick way is to add insulation just to the bottom of the rafters (i.e. leave the entire depth of the rafters as a ventilated gap).  This avoids thermal bridges and means you don't have to cut the insulation into ~400mm panels to fit between the rafters.  But you lose height.
Disadvantages:
  • Attention needs to be paid to allowing the rafters to breath whilst preventing draughts getting into the loft space (this is critically important and is tricky to achieve)
  • You may have to add additional vents at the ridge (see comment from davidfreeborough below)
  • Requires a greater area of insulation and a greater thickness to achieve the same performance compared with insulating the loft floor (see comment from davidfreeborough below)

To quote user "betterroof" on GBF:

"ideally you want a constant unbroken insulation layer, either cavity or internal/external tied into the roof insulation. it's a waste of time otherwise as you'll let all the heat out at the junction between the two. This why we mostly have cold roofs as it's easier to detail. "

To quote user "davidfreeborough" on GBF (my emphasis):

[I asked "If we're going the route of insulating under the rafters, does this mean that we have to add vents at the ridge prior to installing the insulation? Or is the ridge in an old Victorian roof sufficiently draughty?!". David responded:]

It will depend upon the particular roof. Some have a mortar bedded verge which is pretty much airtight, others have loose fitting ridge tiles. 

Do the houses typically have roofing felt below the tiles? If not then you may get enough air movement through the tiles close to the ridge without specific vents.

The disadvantage of insulating at rafter level (warm roof) rather than on the loft floor (cold roof) is that you need a lot more insulation for the same thermal performance. There's a double whammy because the area to be covered is Cosine(roof pitch) times larger & so the insulation thickness for the same thermal performance is Cosine(roof pitch) times thicker. 

It makes sense if you're gaining extra habitable floor space, I'm not sure it makes sense for loft storage. That combined with the sealing issues at the eaves highlighted by betterroof mean that a cold roof may be more appropriate.

 

6) Convert the loft into a proper "room"(!)

Insulating between the rafters gets you part way towards converting the loft into a "proper" room.

 

 
So, there are some of the technical options.  Insulating lofts isn't as simple as it first looks.  We need to ensure that we don't recommend any techniques that will cause ventilation / damp problems in the future.
 
As is often the case, the technical issues are just half the challenge.  I suspect that I'm not the only person who wouldn't want a volunteer to organise the junk in their loft.  When I finally get round to insulating my loft, I'll want to use the opportunity to organise and tidy up our junk, and I'm the only person who can do that.  In fact, I'd be very nervous about letting volunteers / inexperienced installers up in my loft to do anything; it's all too easy to put a foot through the plasterboard.

Will volunteers really want to go up into lofts?  We have a hard enough time recruiting volunteers for draught proofing.  Working in lofts is dirty, potentially dangerous, stuffy, dark, cramped.

Links

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#2

Submitted by Anonymous (not verified) on Thu, 22/04/2010 - 12:14pm.

I think we have to be careful here else we might put people off.

The standard practice I have seen is to insulate up to the top of the joists, then top it up by rolling out further insulation at 90 degrees from the original. As long as this doesn’t get stuffed right up to the eaves, this works fine, all the joist are under the insulation so receive heat from the house.  Wiring almost always finishes under the insulation, because it would require re wiring to put it on top, heating of lighting wiring is highly unlightly, and trapped between two layers of flame proof Rockwool I really don’t see a problem, it’s one of those exaggerated health and safety things that seem to be designed to stop us doing anything, ancient wiring is something far more dangerous. In summer lofts get very hot so that should help them to dry out.

Things get more complex if people want to use their lofts and or deck them out, here maybe it would be better to insulate between the timbers of the roof using foam slabs, whilst still taking care to let the eaves breath.

 

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#3

Submitted by Jack on Sat, 24/04/2010 - 12:45am.

Many thanks for your reply.  It's fantastic to get your advice.

You're absolutely right that we need to tread a cautious line between providing adequate, responsible information and proving so much information that we put people off.  The document above isn't really meant as a public advice document; it's for our own planning purposes.

As you say, if the loft isn't being used for storage then it's relatively trivial to top up the insulation.  But  the problem is that many local lofts quite possibly are full of junk and hence we need to consider how to cope with those lofts.

Regarding insulating the rafters...

Firstly, for other people following this discussion who may need some clarification on the names of the structural elements in a roof, here's a photo illustrating what we mean by "rafters":

The "rafters" in this wonderful old photo are the thick bits of wood (decorated with white paint) holding the roof up, running diagonally in this photo from the top left.  So insulating between the rafters would mean insulating the space immediately beneath the roof itself.

I do wonder whether insulating between the rafters would have much effect on reducing heat loss from the house.  My understanding is that the loft space is ventilated to the outside via the eaves, hence the air volume in the loft will be kept relatively cold.  Heat coming up from the house will transfer to the air in the loft space and then drift out through the eaves, before the heat even gets to the insulation between the rafters.  Yes, if the insulation was foil-backed then it might reflect some of the heat that radiates off the top of the ceiling, but I presume that most of the heat coming up through the ceiling will conduct into the air volume rather than radiate up to the rafters.  Or have I got this wrong?

Insulating the rafters hasn't yet come up in the technical discussion on the Green Building Forum (although that's not to say it wont work, of course).  I'll raise the question on GBF now.

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#4

Submitted by Jack on Sat, 24/04/2010 - 2:18pm.

There has been a good reply on GBF.

Ah, OK, I understand.  The aim sounds like it would be to insulate between the rafters, leaving a 50mm gap between the top of the insulation and the roof covering.  It's this 50mm gap that would be ventilated.  So you'd need to take care to ensure the eaves ventilation only sends draughts into the 50mm gap, not the loft.

I'll add an entry to the document above.  This option sounds quite favourable now.

Many thanks.

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#5

Submitted by Anonymous on Sat, 24/04/2010 - 2:51pm.

I agree using lofts for storage and decking them out is the real problem. I have surveyed 300 odd homes and about a third of the residents didn’t want to insulate their lofts because they were using them for storage etc.  I guess insulating the between the rafters is a compromise, though all “rooms” should have some ventilation / air changes. 

I have seen properties insulated to the top of the existing joists, then new joists added on top at 90 degrees to the originals then filled with insulation and decked. The problem here might be that the additional joists won’t get much heat from the house, not to mention all the additional weight.

Another way to look at this would be to say, as people seem to want to use their lofts as an additional room, maybe we should look in to how to do that properly, that is make the loft in to a room?

 

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#6

Submitted by Jack on Sun, 25/04/2010 - 11:51am.

Many thanks for the reply; really really useful info.  I've added your comments to the document above.

(Eventually I'll tidy up the document above, make it more friendly and post it to EnviroWiki so it's really easy for anyone to edit).

By the way, the discussion on Green Building Forum is continuing.  There's a really, really interesting case study reported on Green Building Forum by user wookey where he uses "technique 2" (i.e. leave the rockwool between the joists, lay ply over the joists, then lay rigid foam over the ply, then lay another layer of ply over the insulation).  Recommended reading.  The bottom line: it seems to work; and airtightness is important.

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#7

Submitted by anna on Mon, 26/04/2010 - 2:42pm.

A quick post of the motivations behind doing a Loft Insulation project:

You might then ask "why not choose an easier problem to start with?".  The problem is that loft insulation is the "easy" problem, no? If you think of any of the other measures we need to implement in our homes - solid wall insulation, air source heat pumps, solar thermal, whatever - those are even more difficult.  And equally complex [= dynamic, interactive, with many different levels of scale etc].  Moreover, I see the attempt to address people's behaviour outside of their physical environment entirely misplaced; there really is a limit to what you can do given that the available loft insulation schemes for instance don't address the reality of people's lives or the physicality of their buildings.

Given that the govt is now prepared to accept that the likes of Tesco and M&S will roll-out loft insulation en masse, one might ask "why bother?".  The answer is that [a] both Tesco and M&S are used to selling products off the shelf, rather than delivering on individualised project implementation at scale, so I doubt the business model will work, and [b] if we pay private companies for loft insulation, then we will have a lot less money available for all the other energy measures we need - including microgeneration.  Thus, whilst the amount of community involvement in actual delivery of a loft insulation project will be small, us doing it ourselves helps us build our own energy security and community resilience.  We need to make the case for this as part of our engaging people in the project.

The conclusion I come to is that we therefore need proper funding to be able even to attempt it, and that we need to make that case to a variety of organisations [Energy Saving Trust, Institute for Public Policy Research etc].

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#8

Submitted by Jack on Mon, 26/04/2010 - 2:51pm.

Many thanks, Anna.  Perfectly put.

I'll quote your post on the introductory page about the Loft Insulation project (assuming that's OK?)

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#9

Submitted by lukasz on Sat, 08/05/2010 - 11:04am.

There is another option for 'unventilated' loft insulation where vapour control layer is incorporated in the ceiling - http://www.greenspec.co.uk/html/refurb/loft_insulation.html.

This is the option I will be opting for myslef as airtightnes is a key in getting to passive haus standard + removing eaves ventilators will allow me to pack the insulation tight to reduce thermal bridging in that area. 

I am expecting a 'fiddly work' in getting the ceiling membrane continous in existing house.

 

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#10

Submitted by TimSG (not verified) on Tue, 23/11/2010 - 3:02pm.

I'm looking at setting up a loft insulation scheme in a conservation area in Westminster again with 3" joists and I'm going to take a look at this as a possible solution

http://www.loftinsulationbridgend.co.uk/Easy-Stack.htm

Relatively affordable - open mesh and sitting 30mm clear of insulation avoids condensation issues associated with full boarding - provides ~4m2 and holds 100kg.

Slightly concerned that the frame as shown in the photo places all of the weight on two joists - will try and get a structural engineer's view - maybe either rotating the frame by 90 degrees or adding more legs to allow fixing to more joists would help spread the weight/increase the weight bearing capacity? 

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#11

Submitted by Jack on Thu, 25/11/2010 - 1:56pm.

Looks like an interesting solution, many thanks for sharing.  Please do let us know how you get on.

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#12

Submitted by Anonymous (not verified) on Sat, 19/11/2011 - 4:19pm.

 Looks really interesting, how did you get on in the end? allergy

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#13

Submitted by Roofing Manchester (not verified) on Tue, 20/12/2011 - 8:50am.

I will also searching to fill the ventilation of my house. I got some idea from your post. Thanks for sharing. If you have some more then  please tell me.

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#14

Submitted by Loft conversions Hertfordshire (not verified) on Sat, 11/02/2012 - 8:17pm.

Some Great Information As I do Loft conversions in hertfordshire ill be take some of this in to work tomorrow Thanks

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