Insulation.....

[Duchess]

Hi all, before I get a roofer in i thought I would ask your opinion... My timber framed building dates from 1500 with a tiled roof it has a breathable membrane on the inside but no other insulation between the rafters, it is quite noisy with the high winds and I was hoping to cut some of that out, but not if it would cause harm to my lil' ole' cottage.

I know how you all love a pic any advice please??

 

[Feltwell]

You can insulate it without causing any harm but it depends on if you want to see those rafters or not.

Is this in a loft that is not normally accessible, i.e. only through a hatch? If it is, chances are it would be much easier & cheaper to insulate the "floor" of the loft instead.

 

[Duchess]

Morning, yes it is accessible through a hatch, but the floor has already been insulated and boarded, tbf this was done by previous owners so I don't know how good the insulation is, I dont have a preference about seeing the rafters, as long as it is not causing damage to them, i don't venture into the loft that often....only on mice missions :evil:

 

[Feltwell]

If the floor has already been done (might be worth lifting a board to check how well) and you don't have any sloping ceilings in your upstairs rooms, there would be no point in insulating under / between the rafters.

Even if the floor is not a good job, chances are it would still be cheaper and easier to take the floor up and add to / redo the insulation there than to do it at rafter level. Why would you want to heat an empty loft space? Noise insulation is harder to crack though. Is the loft hatch well sealed & insulated?

 

[Lime]

As far as noise reduction is concerned you would be far better off removing the insulation on the "floor" of the loft and replacing it with an equivalent depth of vermiculite or similar.
Vermiculite has excellent sound deadening qualities from my own experience of substitution in a loft.

 

[tycarregydwr]

Definitely worth checking how the loft floor is insulated - to what depth and how tightly it's all laid, it might be only a few cm of insulation.

 

[Duchess]

Thanks for your reply, def looking into vermiculite, don't want to spend money on something I don't need!! Thanks for your experience and replies!

 

[FamilyWiggs]

If the "floor" of the loft is already well insulated, then there is no point insulating between the rafters as your loft should then be a cold space. As to noise, are you sure the wind is heard through the loft (could be the hatch I suppose) ?

 

[DJH]

As I’ve stripped the roofs off here on my place to replace with natural slate on the house and asbestos type ones on the subservient buildings, I’ve used the opportunity to fit warm insulated roofs on them.
The reasoning behind this is mainly threefold.

• It has given the opportunity to expose the existing roof timbe rwork to view from below.
• The internal structure will stay warm and dry.
• Air can circulate under the slates extending the life of them considerably.

For roof spaces with a ceiling below, an added bonus is that tanks and pipework located in a roof space are less likely to freeze and there’s no need for a howling gale through the roof space from the obligatory ventilation along with deterioration of all those things we need to keep that are in a heap up there.

The method of construction is to cover the rafters over with either boards or sheets of ply depending on the finish you want to see from below. It’s best to paint or stain these boards or sheets before fixing them, and also do the same to the rafters while they are accessible. Next job is to place rigid sheets of insulation such as Kingspan (yes I know, not exactly green!!) sealing the joints with either a suitable mastic or the tape available for this purpose. These are then covered with a breathable membrane which allows moist air through one way but not water the other way.

This is fixed by 2 x 1 inch pressure treated counter- batten running up the roof with the rafters using either stainless steel proprietary nail type fixings or stainless screws. The 2 x 2 treated slate or tile battens are fixed to these counter-battens in the traditional way.

With insect proof ventilation grills fitted at the eaves you now have a warm ventilated roof where air travels freely under the roof covering dissipating any moist air that manages to get through the insulation or water that might get through the roof covering at any time. The underside of the slates remains dry and don’t crumble or laminate into the white dusty state that anyone who has stripped an old slate roof will recognise.

Some pictures of our bedroom and the new living room extension.

The boards run cross ways over rafters





I've omitted rafters in this room so the boards run with the roof.

 

[stuart45]

I used a similar method on the roof of my extension, although I had 2x2 for the counter battens and 2x1 or the slate battens. Getting the fixings through the 2x2 and 4.5 inches of celotex into the rafters can be quite a tricky job. The advantage of over the top and not inbetween is the lack of cold bridging and is getting more popular now.

 

[MdB]

For our new extension we have 120mm between the trusses and 60mm over the top. This allowed the use of 130m screws to go through the counter batten, insulation, sterling board (to add stiffness) and into the rafter.

 

[DJH]

I should have added that there should be a vapour barrier between the boarding and insulation. This is achieved if you use insulation which has a foil surface and then
tape or mastic the joints together.

The reason I use 25 mm thick batten as counter battens is to give less depth for fixings to go through and to make maximum use of the fixings used. The thicker roofing battens are much sturdier for fixing slates or tiles to yet still maintain a good ventilation gap above the breather membrane and insulation. It's also in important to start at the eaves of the roof, before laying the breather membrane, with a good quality length of say 18" DPC arranging it to lay into the eaves gutter. The breather membrane should not be subjected to sunlight as it will degrade and, because it's a light material it can flap in the wind and end up being shredded.

 

[Lime]

What is to stop condensation forming on the underside of the tape where there are slight gaps in the insulation?

 

[DJH]

Nothing really, that's why I suggested a suitable mastic for the joints. The moisture would soon dissipate when the conditions that formed it in the first place alter like, for example, after a shower or bath when the steam goes after a while. Under normal construction methods it's nearly impossible to maintain the integrity of a vapour barrier but the trade-off in keeping the structure of the property warm and dry is worth it I believe.

This type of roofing method, The Warm Ventilated Roof, is being used much more now especially under metal roof coverings where underside condensation can occur many times during certain weather conditions such as strong sunshine, a heavy downpour followed by sunshine almost immediately. Interstitial condensation can occur during night radiation say on a starry night.

In my mind I like the idea of extending the life of the roof covering by using this method and also the option it gives of exposing the roof structure in the room below.

Later... I should have added that it is possible but fiddly to apply tape to the underside of the insulation but as I said it's very awkward preventing the sticky side from dust and bits of insulation that are flying around! 8)