Welcome to the FAQ’s

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

Are there EWI options for partially filled cavities that cannot be fully filled?

Not really. In partially filled
cavities the boards are
‘flopped around’ so there is a
lot of thermal bypass going on
because the boards are not in
intimate contact with the inner
leaf which they would need to
be to work properly, and so
cold air can circulate on the
warm side of the boards.

In blocks of flats (top floor flats) with flat roofs – where it is not feasible to access the small roof voids on the top floor due to no available access hatch, how do we determine the presence of insulation in the first instance without some form of intrusive inspection and damaging people’s homes/ ceilings? We cannot report correctly to allow an adequate design at present. To ensure a complete building ‘fabric wrap’ this void space would need insulating but may not offer the possibilities to do so internally, leaving only external flat roof insulation which will add to the project costs considerably

Where there is no access to the roof space there is a default in RdSAP: you tell it there
is no access and RdSAP will default to the uValue that would have been required
at the time the building was built. So, it uses the age and the construction type and
looks back at the building regulations and defaults a uValue. It does not mean that
insulation is there so you are taking a risk that the SAP default is something you
can rely on for the Improvement Option Evaluation and Design. The other option is
to insulate the existing roof with a new finish, although this is an expensive option,
but it is much better to do a warm roof than a cold roof and it’s certainly less risky.

In blocks of flats that have a ‘narrow cavity’ (40mm) wall to the un-heated corridor, can the ‘narrow cavity’ to the UHC be filled with expanded polystyrene beads to satisfy PAS2035 and be signed off as compliant or can the narrow cavity be insulated with EWI directly? Will the UHC be considered a fail if left uninsulated?

There is nothing in PAS 2035
that says everything must
be insulated, that will be in
the scheme’s rules that is
providing the funding. If it’s
a heat-loss wall, it would be
good practice to ensure it is
insulated to some standard
and not just the external walls.

Is there a definitive document list on TrustMark of what is required for a successful lodgement/audit?

There is a lodgement guide
that is published on the
TrustMark website with seven
mandatory documents.

We have some properties where the windows are unsuitable for trickle vents due to age and heritage factors – is PIV alongside DMEV an option?

Using wall vents rather than trickle vents is much better because they don’t get
covered by curtains so are always a preferable way of providing air inlets and
background ventilation. Using PIV is an option but doesn’t seem to deliver the
ventilation rates that the building regulations would require and neither does DMEV,
except for the newer fans.

In blocks of flats that have a ‘narrow cavity’ (40mm) wall to the un-heated corridor, can the ‘narrow cavity’ to the UHC be filled with expanded polystyrene beads to satisfy PAS2035 and be signed off as compliant or can the narrow cavity be insulated with EWI directly? Will the UHC be considered a fail if left uninsulated?

There is nothing in PAS 2035
that says everything must
be insulated, that will be in
the scheme’s rules that is
providing the funding. If it’s
a heat-loss wall, it would be
good practice to ensure it is
insulated to some standard
and not just the external walls.

If a cavity wall has been filled and then we’re looking to add external wall insulation, is this possibly a high-risk strategy? Plus, if you’re looking to extract the existing cavity insulation and refilling it, would you need to leave empty for a period of time to allow the walls to dry out?

It’s perfectly okay to put EWI on a cavity wall that has been filled but not on to a wall
that hasn’t been filled (or refilled). If it’s apparent that the wall is wet, you need to
dry it out first because the EWI will stop the moisture travelling outwards so instead
it will move inwards causing damp and mould problems. There is guidance from
SWIGA on EWI and cavity walls. Partially filled cavity walls are a special case – they
are nearly all defective, and the only further insulation option is IWI.

Fabric first: A number of my clients wish to get moving with the installation of an ASHP (to get off gas) while continuing to increase the insulation incrementally, as they can afford it and cope with disruption. Could the Retrofit Academy give some pointers about initial sizing of HP, flow rate, cylinder and radiators with a view to gradually diminishing demand?

The simple answer is no,
you would need a heat pump
engineer to do that for you.
Installing an ASHP now
will increase costs but not
reduce emissions, because
the electricity grid will not be
decarbonised for some time.
Your clients are well advised to reduce
demand as much as they can afford to
at this time, or at least to insulate at the
same time as installing heat pumps.

The CoreLogic PAS App gives you the option to enter ‘not known’ for existing extractor fan flow rates. If we select this option is the retrofit assessment still PAS2035 compliant?

There are devices available that allow you to test for flow rates, but a reasonable
assumption would be that if it’s a bathroom or kitchen fan it would have met the
requirements when it was installed. You can always check for flow rates online too,
if you know the make and model number.

My understanding of PAS2035 is that if you carry out work that changes the air permeability of the building you must ensure that there is a compliant ventilation system in place. If a PVCu, single glazed window, with a draught seal, is replaced by a PVCu double glazed window I don’t believe you are changing the air permeability and so wouldn’t need to install a ventilation system? However, if the new windows had trickles, and the old ones didn’t, you are changing the air permeability in the “right direction”. Would this also commit you to installing the rest of a ventilation package?

PAS 2035 section C.1.4 says: When installing any insulation or air-tightness
measures, or replacing windows, in existing buildings, the adequacy of the existing
ventilation shall be assessed and if necessary improved. So you do need to do the
ventilation assessment, but given the changes described, it seems unlikely that
you would need to do a ventilation upgrade unless there are any other measures at
play or the ventilation system in the dwelling is incomplete or not working.

Are trickle vents only required in habitable rooms and do PIV systems require trickle vents/ air bricks?

In most ventilation systems
(which are extract based) you
only require trickle vents in
the habitable rooms because
the purpose of these is a)
to provide air inlets, and
b) to provide wind-driven
background ventilation when
intermittent extract fans are not operating. If
the ventilation is intermittent, it is a good idea
to include trickle ventilators in the wet rooms.
If you are using PIV, you need trickle vents to
allow air out, particularly from the wet rooms, so
they should be installed in all rooms, including
wet rooms. Not installing trickle vents with PIV
is likely to increase the moisture risk, and is not
recommended.

It’s all well and good having these standards to which we all need to adhere when using funding. However, when it is a client who is able to pay then all these standards and procedures do not apply at all. So how does this then help getting towards the targets and ensuring good quality work is done when there are standards and rules for one side of the coin and none for the other side?

BEIS have said that as more subsidy schemes are introduced, they will require
subsidised work to comply with PAS 2035. BEIS is also working with the finance
industry to encourage lenders to insist on standards like PAS 2035 when they fund
retrofit. All we can do as an industry is give advice on the best way to do it. At
present, the case for able-to-pay households to require compliance with PAS 2035
is that they will get a better job and will expose their homes and health to less risk.
This is a message the Government could send!

Any news on the underfloor cross ventilation fan MEV-ECO?

It is in discussion. There have
been issues with underfloor
insulation that has been done
in conjunction with boilers
which have failed technical
monitoring because there is
no cross-floor ventilation. A
question that is being looked
at is “can the functional
requirements of Part C be met
by mechanical ventilation in
isolated floors?”

The way I read PAS is that you need one complete ventilation system ie dMEV’s in all wet rooms or IEVs in all wet rooms but not a mixture. But some installers believe properties can have a mixture of dMEVs and IEVs. Who is correct please?

The options listed in PAS 2035
do not include a mixture. Some
competent designers may
offer this as a solution, but the
blanket response to this is not
to mix.

Do we have an update on when the new Designer requirements will be live? Also, can you confirm if it will be a requirement to have designer qualifications for Pathway B jobs with this amendment regardless of if it is traditional or conventional.

Colin King sits on the steering group for this and has said the new version of PAS2035
has been released but as far as he is aware this item is not covered.

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