Fire regs for loft coversion - help please!

[sapahesi]

Hi folks

We had plans drawn up for a loft conversion in 1997, which were passed by the BCO, but we didn't go ahead with the work due to finances at the time.

Some 13 years later(!!) we are now going to have the loft converted. We've submiited the old plans for approval as the structure will be exactly the same. However the BCO has asked us to provide further information and/or make changes, as the fire regs have changed since then. Unfortunately the architect who drew up our plans has retired so we can't go back to him to have these amendments made, so I'm trying to work it out myself.

I've managed to fathom out that we need FD20 door thoughout the house, self closers aren't required any longer, and that we need a mains operated fire alam installed. No problem with that. What I'm struggling with is the fire rated gyproc board and insulation for the walls and ceilings. The BCO has said the external walls need to be U rated to 0.3 and the ceiling needs to be U rated to 0.22.

Can someone please tell me if we can still have 12mm gyproc as stated on our original plan? What thickness does the insulation have to be?

Many thanks from a complete novice!

 

[freddiemercurystwin]

Which walls are you talking about exactly, the dwarf walls around the perimeter of the new loft rooms and the ceiling of the new loft? This may help //www.diynot.com/forums/viewtopic.php?p=1592058#1592058

 

[sapahesi]

The BCO stated:

"the method of insulating the external walling doesn't provide the required U value of 0.3" - so this would be the dwarf wall, yes?

and

"the method of insulating the horizontal and sloping ceilings doesn't provide the required U value of 0.22" - which is as it says on the tin!

BTW I should have mentioned the converted room will be a bedroom.

 

[freddiemercurystwin]

I have never used those figures you have quoted for the elements you describe hence my query.

For the loft ceiling I have always used 0.20
For the dwarf walls I have also always also used 0.20

The 0.22 to which you refer is for floors (ie a ground floor) so that's definitely an error on behalf of Building Control.

The 0.30 to which you refer is for a wall however most Building Control Inspectors I have dealt with have considered that the dwarf walls in a loft should be considered part of the roof hence they ask for 0.20.

Below is a typical loft conversion detail showing the required insulation to achieve 0.20 for the dwarf walls and the ceilings.

Untitled

• freddiemercurystwin
• 8 Jun 2010
• 20

If however you are confident that the inspector has not made any errors you will need to contact the technical advisor's of your chosen insulation provider. I use Kingspan as most builders (in my area) tell me that its the cheapest and readily available. Handily they also have the best techy helpline 01544 387 382. Give them a ring on and they will do a quick U value check and tell you exactly what you need to know. If you ask they will also send you an email confirmation of the calculation you can shove under the nose of your inspector if he asks. The whole process will take no longer than 10 minutes. If/when you ring them, you'll have to press a button or two but press the button for the Architects or Specifiers option.

Someone wrote on the Forum recently that they'd managed to install a mains fire alarm in all habitable rooms instead of upgrading all of the doors and had it approved so that may be a preferable choice if your inspector is in agreement.

Did you have specific questions relating to the plaster board choice for fire protection?

 

[sapahesi]

Thanks FMT, that's really helpful. I wouldn't have known (or expected) there to be any errors on the BCO's part, so I will ring them and query that part of the schedule

What I need to know now is what thickness board I need, I gather the standard is 12mm, is this sufficient and do we need any other insulation material in addition to this?

 

[freddiemercurystwin]

For the walls and ceiling in the loft 12mm board will be fine. For the floor between the first floor and the loft the existing ceiling boards usually satisfy Building Regs provided you use T&G boards for the floor. Building Control don't like lathe and plaster much though so if your ceiling is of that construction they may insist on an additional layer of board for the ceiling or other upgrade. You can get away with chipboard for the floor but it is frowned upon as it tends to squeak and if it ever gets wet it will likely need to be replaced. If you have an ensuite going in there it would be prudent to use ply, there is also a risk from a leak in the roof or a radiator pipe.

 

[sapahesi]

That's great FMT, thank you SO much

I have just fired an email off to the BCO with lots of queries, they will probably hate me now but hey ho, if it makes life easier (and a tad cheaper) in the long run....!

Unfortunately our ceilings are lathe and plaster, being a 1930's built house. There's no ensuite going in the loft but I take your point about the floor re radiator leaks, but hopefully my builder should be able to work that out for us.

Been a bit of a nightmare trying to read the architect's spec on the drawings, but think I've got it all down OK. Wait and see time I guess. Now to get hubby and his Technical Drawing 'O' level to redraw the plans - we realised 13 years too late that the velux windows have been drawn on the wrong side of the house as well as a couple of other minor amendments that are needed.