Cavity barriers behind box profile sheeting

[Nealt]

We have built a timber framed house, clad walls and roof with box profile sheets, no soffits on the roof. We were initially asked how we were venting the underside of the roof sheets without soffits. So we argued that air is drawn across the roof through the gable end walls sheets. Now BC are asking hows that going to work when cavity barriers are required behind wall sheets. We have not fitted any cavity barriers. Is this a valid requirement 

[Iceverge]

Lovely house. 

 

I don't know how to passify the BC but if you have done a good job with Airtightness you won't have any issues with moisture. 

 

The only reason for requiring a hurricane of wind blowing through people's roof is because they make a completely inadequate attempt to air seal and correctly ventilate the interior. 

 

The profiles cladding can ventilate above the chutes at both sides anyway and that ridge won't be airtight. 

 

I can't see any issues.

[Nealt]

Hi Iceverge, thanks for your response. We have had airtest done and its 0.5ACH so within passivhaus standards and we have MVHR. Weve been telling the BC people that no moist air is coming from inside but they keep hitting us with the building standards requirements

[Iceverge]

It's the roof they'll be worried about. 

 

Do some sums to show an adequate free area in the "up"ridges of the sheeting. And how they match the open space under the ridge cap. 

 

It'll be more than sufficient to ventilate the roof. 

[Nealt]

Weve done that and now they are asking about cavity barriers, so they say we should have cavity barriers and so the airflow will be restricted by the barriers

[Iceverge]

You've lost me. 

 

The profiled sheets having ventilation above the guttering will be adequate for the roof. 

 

What has cavity barriers in the gable ends got to do with it. 

[Nealt]

We have put the profiled foam infill pieces at the top and bottom of roof sheets as per manufacturer. So now the BC inspector says that has blocked of that means of ventilation. So we were proposing that the roof sheets are cross ventilated by air coming up through the gable end sheets. Now hes asking how will that work if you have cavity barriers

[Iceverge]

Can you pull them out until you have enough ventilation space?

 

Maybe when the BC is gone shove something in there like this to stop the bugs. 

 

[Russell griffiths]

Do you mean cavity barrier for fire protection. 
if so we have a letter from bc saying we do not require them as it’s a single storey dwelling with no neighbours. 
and not near the property boundary. 

[saveasteading]

Is this single metal sheets on suspended timber battens?

What do you see when looking up at the roof underside?

A sketch would save more questions.

[Nealt]

  On 07/12/2024 at 14:12, Russell griffiths said:

Do you mean cavity barrier for fire protection. 
if so we have a letter from bc saying we do not require them as it’s a single storey dwelling with no neighbours. 
and not near the property boundary. 

Expand  

Thanks Russell, yes they are supposed to prevent smoke and fire spreading.  We havent fitted them, but the BC guy is saying we should have them because its in regs. Is your house clad with box profile sheeting

[Russell griffiths]

  On 08/12/2024 at 09:15, Nealt said:

Thanks Russell, yes they are supposed to prevent smoke and fire spreading.  We havent fitted them, but the BC guy is saying we should have them because its in regs. Is your house clad with box profile sheeting

Expand  

Mine is clad in timber. 
my bc said it’s only to stop the spread of fire if you have a second floor, as mine is only single storey, then there’s nobody up stairs to protect. 
 

[ADLIan]

Cavity barrier may be required to separate any wall cavity from any roof cavity even in this instance. BCO interprets and enforces Regs so his call here.