MVHR retrofit requirements?

[oliviaaa999]

Hello everyone, we are currently renovating a 1960's bungalow as our first property and we're hoping to future proof and make it as comfortable to live in as possible. 

One of the additions we're considering is a MVHR system as I hate having windows open (not a fan of insects!) as well as hopefully the heat retention benefits. I'm researching what we would need to do to to maximise the benefits, especially in regards to insulation and air-tightness. 

 

I've tried having some insulation companies round but there aren't really any in our area, the two people we've had round didn't know about anything other than loft and wall cavity insulation. They both said spray foam, one of them mentioned that the new regs for it are improved and that there's a new way of doing it between roof joists so still need to look into that, but a bit wary as he was a bit 'sales-y'. 

 

The house is currently been stripped of carpets and wallpaper and the next stage will be rewire, then skim and suites/kitchen fitted. The house has no bathroom vents fitted so I'm hoping to make a decision on the vent system before the rewire so we know whether or not to include extractor fans.

 

We will be eventually replacing all the windows + the doors but I'm looking for an exact list of steps to take to improve the home. For example, what types of insulation are required (loft, floor, wall etc) and how do you retrofit airtightness? Is it something I can do once the skimming is done or is it best done as early as possible? Do I need specific backboxes for the sockets, does it need specific plumbing techniques when putting in rads/bathroom suites, etc. I'm hoping that sealing the house up will also help with reducing the number of insects coming in too, but it's a bit of an overwhelming task to start on as there are gaps everywhere (under doors, between floorboards, where the wall meets ceiling/floor)

 

Some more info:

- Location is near a forest and not too close to any main roads

- Suspended timber floors with a massive underfloor cavity, 5ft in some areas. Not sure if this would need to be insulated/air-tight?

- Only appx 800 sqft so not a huge system is required

- I think I've seen some dot and dab plaster on the walls, not sure if this effects what we're able to do?

 

To sum up, here are some Qs I have

- Is underfloor insulation necessary, if so then can this be done via the cavity by putting insulation in-between the joists or will we need to lift all the floorboards in each room?

- Are we okay to leave the current cavity wall insulation (old and maybe not as efficient but maybe better than nothing), or does this need removing and replacing?

- For loft insulation, should we insulate the roof, floor or both? Is there anything specific recommended for MVHR loft insulation?

- What are the small details for retrofitting airtightness that are easily missed?

- How to retrofit airtightness on the larger areas like roof, walls and floors? Do I just go round with expanding foam for every crack I see?

 

Thank you so much!

[JohnMo]

Hi, sounds like lots of working going on. I would split your questions into different topics each in it's relevant section, otherwise you will not get many answers that make much sense in a weeks time. So take all those questions not related to MVHR and repost.

 

So looking at the ventilation, no ventilation gets you away from opening windows when it's hot. Flow rates are not sufficient for that. It will help a little but generally not much.

 

There are three plausible ventilation strategies.

 

MVHR - mechanical ventilation for supply and extract with heat recovery. This runs all the time and is an addition to any leaks within the building fabric. To get the best from this system the house needs a reasonable airtightness. Filters can be expensive depending on unit used.

 

MEV - mechanical extract only. Trickle vents in windows or walls. Would only use this system if trickle vents are humidity controlled AND extract points are also humidity controlled AND fan speed  is controlled on a constant pressure. Easier to install than MVHR, one fan instead of two. Only runs when needed so heat loss is minimal. No filters to replace in theory, but would install with filter socks in extract points.

 

dMEV, easiest to implement, similar to above but each wet room has its own fan. Inlet devises as per MEV. No filters

 

All the above require internal door undercuts of around 10mm to proved a ventilation route if doors are closed.

 

All will give good humidity control, should be near silent in operation. All have a compromise cost/difficulty of install, weighted against ongoing running cost (electric and filter) and heating cost.

[Russell griffiths]

Hi

you need to stop and get some questions answered first. 
do not organise the re wire yet, it could definitely get in the way of future work. 
 

you need a clear picture of what renovations need doing and then a schedule of what goes in first. 
 

I suppose the big question is budget

being as none of us will be coming around to do this work you can be open about your budget and what you want to achieve, also how long are you going to be there. 
is it £10,000 and chuck it back on the market

£25,000 and going to be here 5 years, or long term I want to improve this place as best I can, then some pictures. 
 

without knowing your budget it’s fairly hard to start pointing at the bits where best to spend the money. 
 

you can do some very simple sums and then work out how much you have left for improvements. 
 

 

[oliviaaa999]

9 hours ago, JohnMo said:

Hi, sounds like lots of working going on. I would split your questions into different topics each in it's relevant section, otherwise you will not get many answers that make much sense in a weeks time. So take all those questions not related to MVHR and repost.

 

So looking at the ventilation, no ventilation gets you away from opening windows when it's hot. Flow rates are not sufficient for that. It will help a little but generally not much.

 

There are three plausible ventilation strategies.

 

MVHR - mechanical ventilation for supply and extract with heat recovery. This runs all the time and is an addition to any leaks within the building fabric. To get the best from this system the house needs a reasonable airtightness. Filters can be expensive depending on unit used.

 

MEV - mechanical extract only. Trickle vents in windows or walls. Would only use this system if trickle vents are humidity controlled AND extract points are also humidity controlled AND fan speed  is controlled on a constant pressure. Easier to install than MVHR, one fan instead of two. Only runs when needed so heat loss is minimal. No filters to replace in theory, but would install with filter socks in extract points.

 

dMEV, easiest to implement, similar to above but each wet room has its own fan. Inlet devises as per MEV. No filters

 

All the above require internal door undercuts of around 10mm to proved a ventilation route if doors are closed.

 

All will give good humidity control, should be near silent in operation. All have a compromise cost/difficulty of install, weighted against ongoing running cost (electric and filter) and heating cost.

thanks for the suggestion! I'll break it down and repost later tonight. To answer your responses, I know we'll (unfortunately) need to open windows still but hopefully a lot less if it's just to get fresh air into the house! ☺️ 

I'll explore the MEV and dMEV options further to see if they're more suitable for the situation. I imagine it'll come down to how airtight we think we can get the house as the installation shouldn't be too difficult (small bungalow).

The door undercuts is really helpful info, I'll make a note of that for when it comes to putting in doors!

[oliviaaa999]

6 hours ago, Russell griffiths said:

Hi

you need to stop and get some questions answered first. 
do not organise the re wire yet, it could definitely get in the way of future work. 
 

you need a clear picture of what renovations need doing and then a schedule of what goes in first. 
 

I suppose the big question is budget

being as none of us will be coming around to do this work you can be open about your budget and what you want to achieve, also how long are you going to be there. 
is it £10,000 and chuck it back on the market

£25,000 and going to be here 5 years, or long term I want to improve this place as best I can, then some pictures. 
 

without knowing your budget it’s fairly hard to start pointing at the bits where best to spend the money. 
 

you can do some very simple sums and then work out how much you have left for improvements. 
 

 

Hi Russell! Unfortunately we can't push the rewire back any further or we may lose the builders! But he's just coming in to do sockets, fire alarm, new board etc first fix, nothing to do with an MVHR system yet. Just need to decide if we're going the MVHR so we can tell him to leave out the extractor fans in the bathrooms.

 

We're already spending a ton on everything else on the house so we're hoping to spend the minimum required for the MVHR system (but not skimp out and have it be worthless). Definitely planning on staying long term (at least 10yrs) so we're seeing it as an investment. We've had a quote through for around 1.8k for supply which would be great, but I imagine those are basic models and we may want to upgrade a little (Vent Axia Kinetic BH R/H and a Nuaire unit). Also no idea what the cost would be for airtightness as the house is basically full of holes at the moment. In terms of spending money we're basically looking at costs for each project, figuring out which are priorities/necessary and going from there. Things like replacing windows we're planning on doing at a later stage, installing a boiler and rads is being done now, etc.

 

I was thinking we could worry about the actual MVHR unit later and just focus time, energy and budget on the main building for now (insulation and airtightness) and getting it ready to move in, then install the unit and ducting afterwards (as it's a bungalow we can do it all from the loft). Not sure if I'm mistaken on that assumption though!