[bluGill]

You probably cannot do a renovation the tightens up your house enough to matter. Of course you have not specified what you are doing, it is certainly possible to do that, but it is a major effort that makes the house unlivable for a couple months and costs a lot of money. If you don't do that level of renovation your house will have enough leaks that a ERV will not make any difference in air quality (and even that level doesn't always make the house airtight enough to need an ERV). Making a house airtight is very hard - worth doing because of the energy savings, but not easy.

If you are doing that level of renovation is is probably better to just tear down the house and rebuild. The costs will be similar and there are a lot of other things people demand of a new house layout that cannot be retrofitted in the old shell. Often the law will not allow this and so you are forced to renovate just to keep some now illegal feature that is worth keeping, but otherwise a tear down would be better.

[jonstewart]

You're right in the main, of course, that it takes a major renovation to make an old home tight enough to be worth it, but wrong in your assumptions:

* It's a rowhouse, so there are two party walls on either side.

* Brick.

* The front and back walls are half the length (15') of the party walls.

* The house is small, a footprint of 450 sq ft.

* The renovation will extend the back roof line (pitched roof, front to back).

* The attic (with extended roof) will be renovated with a bedroom and 3/4 bath, plus storage and mechanical.

* Plumbing will be replaced.

* Gas boiler (with radiators) and existing central A/C will be replaced with heat pump.

* We'll be out of the house for months.

* It's in a historic district so it can't be torn down.

* Fortunately most of the windows have been replaced before the historic preservation office started cracking down on replacements. We have light-blocking hex blinds that insulate them nicely at night.

* I will try to sneak in a new front door that's the same design as the old one, and fix up the jambs and sill.

* Historically DC is still more heat dominated than cooling dominated, but climate change is tilting the balance. It may be hard to fight the stack effect in the winter but in the summer I hope to run the house at positive pressure. It's when the A/C's been going for days that the air in the house seems stale.

* Even though there's very little insulation today in the attic (just cellulose strewn between joists), it's not expensive to heat or cool, because it's such a small house.

* I care more about the ERV as a luxury good than as a cost effective appliance. I'm quite sure the cost of it will be negligible when compared to everything else in the reno (we're doing the kitchen, too).

Although the cost will be insane, I expect we'll come close to breaking even on value added to the property, given the neighborhood we're in.

[bluGill]

You have mostly made my point.

You have also touched on why I oppose historical districts. Historical buildings should be something people are required to learn about in their history class.

[jonstewart]

I’m with you there.

[BizarroLand]

Anyone can do a renovation that "tightens up your house enough to matter".

Use a qualified professional. Get multiple inputs.

It will cost money, and more money as you approach perfection, but it is doable.

[bluGill]

Not really as the structrure of most houses leaks. It can be done but you are doing a lot of work that is easy to skip

[BizarroLand]

That is true, and I guess technically you don't want a house with no leaks, only with leaks that you have complete control over.

Spray foam insulation can seal essentially any structure, and it doesn't require much more than a small hole drilled into the wall between the beams which is easily spackled over.

It can also be put on as insulation in attics and crawlspaces.

Combine that with a full ducting audit if any of your ducting pierces the envelope, a full intrusions audit for power boxes and the like, and new windows/house sheathing/ proper roofing, you can get very close to as good as a new built.

Most of these I would not suggest doing as a DIY, therefore I still say it is expensive, and even moreso if you have lathe and plaster instead of more modern drywall or encounter any of a myriad of issues likely to be uncovered when doing these things to a very old house.

[bluGill]

> Spray foam insulation can seal essentially any structure, and it doesn't require much more than a small hole drilled into the wall between the beams which is easily spackled over.

A hard maybe on here. Done right it can of course, but you are depending on it filling the cavity without so much pressure that is breaks the walls. The industry as figured a lot out, but this is still compromise and some guessing and so it won't always work (it usually will). There are also many ways they used to put voids in old houses that would not be reached by this.