Loft hatch, boarding and insulation questions

Spir4L

Hello, I recently got two quotes for adding a hatch (in London, England), improve the insulation, and install boarding on my loft.The two companies seems to use two different ways of raising over the joists to increase the insulation to the 270mm standards:

• one uses a raised leg system (I guess this or similar)

• the other one timber on the joists to raise the height

The price for this part of the job is pretty comparable, so I would think the timber one would be a better solution for better weight distribution.

• Am I wrong?

They also both offered to improve the insulation level to install some insulation between the roof rafters to reduce temporary condensation and improve the temperature in the loft. They seem to use two different but similar options:

• one offered the installation of 50mm PIR Celotex Wrap

• the other one the installation of Rafter insulating membrane SF19 and battening

For this part of the job the price is quite different, with the second option being about £1k more expensive than the first. So opposite to the first part I would be tempted to choose the first company.

A couple of questions here:

• I don't seem to find anywhere online the existence of Celotex wrap but only Celotex boards. Does Celotex wrap even exist?

• is SF19 more expensive or a better solution to justify the price increase?

Thanks in advance!

Boohoo

Spir4L said:

Hello, I recently got two quotes for adding a hatch (in London, England), improve the insulation, and install boarding on my loft.The two companies seems to use two different ways of raising over the joists to increase the insulation to the 270mm standards:

• one uses a raised leg system (I guess this or similar)

• the other one timber on the joists to raise the height

The price for this part of the job is pretty comparable, so I would think the timber one would be a better solution for better weight distribution.

• Am I wrong?

They also both offered to improve the insulation level to install some insulation between the roof rafters to reduce temporary condensation and improve the temperature in the loft. They seem to use two different but similar options:

• one offered the installation of 50mm PIR Celotex Wrap

• the other one the installation of Rafter insulating membrane SF19 and battening

For this part of the job the price is quite different, with the second option being about £1k more expensive than the first. So opposite to the first part I would be tempted to choose the first company.

A couple of questions here:

• I don't seem to find anywhere online the existence of Celotex wrap but only Celotex boards. Does Celotex wrap even exist?

• is SF19 more expensive or a better solution to justify the price increase?

Thanks in advance!

Why would you want to make the loft space warmer?

It's your house but if you go ahead have you thought of how the people are going to get the long timber and loft boards upstairs and into the loft without causing damage.

What insulation do you have up there now and what size are beams that the legs or timber are going to be resting on?

Spir4L

Boohoo said:

Why would you want to make the loft space warmer?

It's your house but if you go ahead have you thought of how the people are going to get the long timber and loft boards upstairs and into the loft without causing damage.

What insulation do you have up there now and what size are beams that the legs or timber are going to be resting on?

Warmer in the winter and colder in the summer I guess, I thought its gonna be good for the items I will store there (for example clothes).

There's currently an access but it's really badly located, so they will probably open the hole for the hatch and then carry up the boards from there? I wasn't thinking they should do much damage to be fair  

At the moment there's 100mm rockwool in plastic bags over the joists. The joists are about 55mm tall and 85mm wide as far as I remember.

diveunderthebonnet

If you mean insulation fitted to the roof trusses i would wait till someone more knowledgeable comments on this thread as there have been several posts about fitting insulation in the rafters that has caused problems ,did you know the loft space is supposed to be cool, yes the rooms below should be warmer due to the insulation fitted to the floor of the roof,as i have said others will be along to give you sound advice so wait before making a potential mistake.

singhini

I'm no expert and so take all my comments with a pinch of salt, but timber risers generally give better load distribution and a more solid floor. Raised-leg systems are fine and widely used, but timber is structurally superior, especially if you plan to store heavy items.

Since the prices are similar, timber probably gives you more long-term robustness. -----> but i could be wrong so bear that in mind. 

I'm not aware of Celotex making a “wrap”. Celotex is a brand of rigid PIR insulation boards (e.g., 50 mm, 75 mm, 100 mm) -----> but i could be wrong so bear that in mind. 

Perhaps the installer means one of the following:

50 mm Celotex PIR boards cut between rafters, or

50 mm foil-faced PIR boards fixed under rafters as a continuous layer, or

50 mm PIR boards used in conjunction with foil tape (sometimes colloquially called “wrapping”).

You should ask the installer exactly what product they mean and get the specification in writing.

Boohoo

diveunderthebonnet said:

If you mean insulation fitted to the roof trusses i would wait till someone more knowledgeable comments on this thread as there have been several posts about fitting insulation in the rafters that has caused problems ,did you know the loft space is supposed to be cool, yes the rooms below should be warmer due to the insulation fitted to the floor of the roof,as i have said others will be along to give you sound advice so wait before making a potential mistake.

OP have a look at this thread about rafter insulation.
https://forums.moneysavingexpert.com/discussion/6640465/roof-problems/p1

Spir4L

diveunderthebonnet said:

If you mean insulation fitted to the roof trusses i would wait till someone more knowledgeable comments on this thread as there have been several posts about fitting insulation in the rafters that has caused problems ,did you know the loft space is supposed to be cool, yes the rooms below should be warmer due to the insulation fitted to the floor of the roof,as i have said others will be along to give you sound advice so wait before making a potential mistake.

This is something they shared with me:

With the upgrading of the loft insulation thickness to a minimum of 270mm it will become warmer on the lower levels of the property, which will automatically leave the loft space a lot colder during the winter months, during a prolonged cold spell of frost and snow this can increase the chance of layers of vapour freezing on top of and under the existing roof membrane and on top of and under the existing roof tiles/slates, when the frozen vapour eventually melts as the temperature warms up it can condensate and create temporary condensation droplets which drop off the membrane and into the loft space.
To combat temporary condensation and further insulate the loft space, you can either install a (50mm Celotex loft wrap to the roof rafters to create an R Value of 2.25m2K/W) or at the very least run a dehumidifier in the loft space at the end of every prolonged cold spell.

Spir4L

singhini said:

I'm no expert and so take all my comments with a pinch of salt, but timber risers generally give better load distribution and a more solid floor. Raised-leg systems are fine and widely used, but timber is structurally superior, especially if you plan to store heavy items.

Since the prices are similar, timber probably gives you more long-term robustness. -----> but i could be wrong so bear that in mind. 

I'm not aware of Celotex making a “wrap”. Celotex is a brand of rigid PIR insulation boards (e.g., 50 mm, 75 mm, 100 mm) -----> but i could be wrong so bear that in mind. 

Perhaps the installer means one of the following:

50 mm Celotex PIR boards cut between rafters, or

50 mm foil-faced PIR boards fixed under rafters as a continuous layer, or

50 mm PIR boards used in conjunction with foil tape (sometimes colloquially called “wrapping”).

You should ask the installer exactly what product they mean and get the specification in writing.

Thank you for this comment I am getting in touch to understand better what it is that they would do! Are you familiar with the celotex and the installation within Rafters?

The post @Boohoo shared is pretty scary to be fair https://forums.moneysavingexpert.com/discussion/6640465/roof-problems/p1

singhini

I thought temporary condensation in lofts during cold snaps is normal and usually harmless.

You only need extra rafter insulation if it’s happening regularly, not just during extreme cold, droplets are large enough to cause staining, there is poor ventilation, or you have warm, moist air leaking into the loft from below (usually the real cause).

Adding PIR under rafters is a secondary measure, the primary fix is ventilation and sealing air leaks.

Installing PIR under rafters warms up the loft slightly, reducing the risk of temporary condensation droplets falling from the membrane.

But it must not:

block ventilation at the eaves

cover up vents

create an unventilated warm roof unless the entire roof is converted to a warm-roof design (which costs thousands). 

You should click the link in Boohoo post and read that thread. 

Tread with caution.

singhini

Spir4L said:

singhini said:

I'm no expert and so take all my comments with a pinch of salt, but timber risers generally give better load distribution and a more solid floor. Raised-leg systems are fine and widely used, but timber is structurally superior, especially if you plan to store heavy items.

Since the prices are similar, timber probably gives you more long-term robustness. -----> but i could be wrong so bear that in mind. 

I'm not aware of Celotex making a “wrap”. Celotex is a brand of rigid PIR insulation boards (e.g., 50 mm, 75 mm, 100 mm) -----> but i could be wrong so bear that in mind. 

Perhaps the installer means one of the following:

50 mm Celotex PIR boards cut between rafters, or

50 mm foil-faced PIR boards fixed under rafters as a continuous layer, or

50 mm PIR boards used in conjunction with foil tape (sometimes colloquially called “wrapping”).

You should ask the installer exactly what product they mean and get the specification in writing.

Thank you for this comment I am getting in touch to understand better what it is that they would do! Are you familiar with the celotex and the installation within Rafters?

The post @Boohoo shared is pretty scary to be fair https://forums.moneysavingexpert.com/discussion/6640465/roof-problems/p1

No, but I was planning something similar i.e. creating extra storage space and improving the warmth in the house. I kept going around in circles with what installers said and what the internet said, not knowing whether I should or shouldn’t go ahead -----> and in the end i didn’t bother.

Swipe

If you have adequate ventilation in your loft you should not be getting any condensation at all, regardless of any cold spells. A good sign is when it's windy, you should be able to feel air circulating when you are up in the loft.