Welcome to the FAQ’s

This section lists some of the many questions Retrofit Academy staff and tutors have been asked over the years.

What guidance is available relating to ventilation?

We have produced
Technical Guidance on
Ventilation, specifically
IEV and DCMEV. This is
available to members, and the
calculators are included in the
PAS Templates.

Is air tightness testing required for all projects?

For Path C, where the retrofit design includes any EEMs for the improvement
of the building fabric (e.g. insulation, air-tightness, replacement windows) and/
or a ventilation upgrade (see Annex C), it shall also include an appropriate air
tightness standard for the dwelling after the work has been completed. There
is also a requirement for the Retrofit Installer to demonstrate compliance with
the air tightness standard by means of an approved test (e.g. fan pressurization
testing) in accordance with the standard published by the Air Tightness Testing and Measurement
Association (ATTMA).
Path B is covered by PAS 9.2.5 and air tightness testing may not be required. Only assessment of
the adequacy of the existing ventilation system and upgrade in accordance with Annex C is.
Path A is covered by PAS 9.1.12.
For all paths, Annex C 3.2 covers where the ventilation is to be upgraded. Testing may be
needed when the ventilation is upgraded. Where intermittent extract ventilation or passive stack
ventilation have been installed as part of the design, a test may be used to show that the air
permeability is greater than 5 m3/m2h at 50pa.

Which Quality Assurance Schemes are considered suitable to reduce the Inherent Technical Risk?

At present, only SWIGA meet
this criteria.
The Insulation Assurance
Authority (IAA) is currently
working on something too.

I have a project where the total number of properties is well above the level for risk path C, but the houses are spread over a 10-15 mile radius from the centre point. The installer has been informed it should be risk path C but does not understand why. If only 15 properties are being refurbished at a time on the same street, would this then make it risk path B?

The more properties a project
contains, there is a higher risk
of error and defects occurring.
This is because replicating
mistakes at scale increases
its impact on residents and
property owners.
The PAS2035 Risk Assessment states that
projects with:
• Fewer than 10 dwellings = Risk Path A
• 11 – 30 dwelllings = Risk Path B
• More than 30 dwellings = Risk Path C
Retrofit Coordinators are reminded that it’s the highest assessed grade across the five criteria that
determines the overall risk path.
So whether or not your project is spread across a wide area or multiple streets, it’s the overall number
of properties that matters

With regard to park home EWI, an installer has advised me that they believe that capping or verge trim can be used on park homes and have been advised that by the IAA. I remember discussing with Colin King and I am of the understanding that roof extensions require to be added. Can you confirm?

Verge trims and cappings are
not compliant with PAS 2035,
and may not be used, even on
park homes. IAA guidance on
this point is incorrect. SWIGA
is preparing new guidance.

In relation to door undercuts what is the situation regarding fire doors in a property and creating a gap, also would putting a ventilation grill on the bottom of fire doors also be an issue?

Yes, fire doors should not have
undercuts or grilles. However,
internal doors are rarely fire
doors, except in HMOs.

Guidance states that properties requiring continuous extract ventilation require background ventilation in all rooms except wet rooms. If a property has existing background ventilation in the wet rooms do we need to remove/seal these up?


With regards to ventilation in kitchens, are cooker hoods acceptable as long as you can ensure they are going to the outer air?

If the intention of the project is to reduce the air permeability of the house below 5
m3/m2hr @ 50 Pa, or it might be reduced below 5 m3/m2hr @ 50 Pa by virtue of the
insulation and/or airtightness measures, then the ventilation has to be upgraded to
a continuous system. It doesn’t have to be dMEV, it could be cMEV, MVHR or PIV,
but PIV is not recommended.
On the cooker hood point, if the cooker hood is an extracting model (not a recirculating model) then
it can be counted as part of an intermittent extract ventilation (IEV) system. It cannot be counted
as part of a continuous ventilation system unless it runs continuously, i.e. 24/7

The new flow chart states we can only omit areas in wet rooms? What about other technical reasons such as narrow/high stairways, narrow hallways, loss of floor area in very small rooms, water tank cupboards, fuse boards etc.?

Good question! There is
less risk in other spaces,
unless they are unheated, but
you should apply the same
principles as are set out in the

I have got IOE and MTIP results for one property using PHPP but am struggling to see how best to present this – columns of numbers are not particularly useful. Will there be more PAS 2035 presentation templates for PHPP modelling?

Yes, The Retrofit Academy Centre of Excellence already has software that covers
improvement option evaluation and medium-term improvement plans, and we are
working to improve the formats. The latest version of the software accepts inputs
from Full SAP or from PHPP.

Installing fixed heating and continuous ventilation in all wet rooms is going to increase the customers energy bills. Do we need to discuss this with customer and get written consent as we can see numerous complaints coming from this.

Of course you need the
customer’s consent – it’s
their home! If you don’t
install the required heating
and ventilation the partial
insulation will lead to
condensation and mould
growth in those rooms, eventually damaging
the building fabric and the occupants’
health. So unless you install the heating and
ventilation you may not install the partial

The flow chart states that if 100% of the property is to be treated then it should be installed with appropriate design standards. What design standards are they referring to and what ventilation measures are needed?

You should use the insulation industry best practice details published by NIA/
SWIGA/INCA and/or the details in the Retrofit Pattern Book published online;
both are referred to in PAS 2035. Your specifications should comply with the
manufacturers’ installation requirements and recommendations, and with the
requirements of the products’ or systems’ BBA certificates.

Do we need to install fixed heating in all wet rooms or just those where we are installing less than 100%?

It has to be possible to heat
the partially insulated or
uninsulated rooms to at least
18oC during the heating

If we test the property and the air permeability of the building envelope has not been reduced below 5 m3/m2h at 50 Pa is intermittent extraction and background ventilation sufficient?

Yes, if you test after you
have installed any proposed
insulation and airtightness

The new flow chart states that all extract ventilation must be continuous. We’ve been working to the original flow chart that stated we only need to install continuous ventilation if there is condensation or mould present. According to the PAS we only need to install continuous ventilation “if the proposed energy efficiency improvement measures are either intended to reduce the air permeability of the building envelope below 5 m3/m2h at 50 Pa or might do so, as existing IEV or PSV as described in C.2.3 shall then be assessed as inadequate”. Should we just be accepting this and fitting continuous ventilation in all properties or should we be testing this?

The new flow chart referred to is the one for use with partial IWI only. The PAS
is correct in all other circumstances, but the new flow chart imposes continuous
ventilation if IWI and/or EWI are not applied to 100% of the wall area of the dwelling.
In all other circumstances, you can use an airtightness test to demonstrate that you
don’t need to upgrade from intermittent to continuous ventilation (i.e. Q50 > 5 m3/
m2hr), but the least risk way of proceeding would be always to install continuous
ventilation. Decentralised mechanical extract ventilation (dMEV) fans are a straight
swap for intermittent fans in wet rooms, and they cost very little more.

T: 0330 055 7629
E: info@retrofitacademy.org
A: Barn 4, Dunston Business Village,
Stafford Road, Stafford, ST18 9AB

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