Why does construction wood stink when it burns?

Factual Questions
1

I regularly use a wood fired pizza oven, for which I buy kiln dried wood marketed as being suitable for pizza ovens.

I recently knocked down an interior wall in my house. The wall was just a timber frame with plaster boards attached to it. The timber looks like regular “2 by 4” wood, unpainted, unremarkable.

I was bored the other day after making pizza so I decided to throw in some of the wood from the timber frame wall. It smelled acrid and disgusting when it burned. I ended up taking it out and dousing it in water, and then throwing in more of the kiln dried wood to cover up the smell. The kiln dried wood smells much more fragrant in comparison.

Is this difference due to some treatment the timber went through or is it because of the kind of wood used?

2

Your kiln dried wood is hardwood. Most studs are softwood, called SPF for Spruce/Pine/Fir because the actual species. Softwood naturally contains more tars and burns quickly giving you at acrid smell and taste.

3

I believe construction wood is treated with a compound containing copper and arsenic to repel termites and prevent rot.

Arsenic-Treated Wood | NCHH

4

I thought that was just the green/pressure treated outdoor stuff you see for building decks or fences.

5

My first thought. The fumes and ash residue of burned CCA-treated wood are toxic.

## CCA-treated timber and fire

Do not burn CCA-treated timber in fireplaces, barbecues, wood stoves or any wood fire.
In the event of a bushfire, the ash from burnt CCA-treated timber can contain up to 10 per cent (by weight) arsenic, chromium and copper.

Swallowing only a few grams of this ash can be harmful. Symptoms can include nausea, vomiting, diarrhoea and a ‘pins and needles’ feeling in the skin. Keep children and pets away from CCA-treated ash until it is removed, and see a doctor if you or anyone in your family shows signs of having eaten CCA-treated ash.

Ash from CCA-treated timber can be double-bagged, sealed and taken directly to your local landfill. When removing CCA treated timber ash, wear protective gloves, disposable overalls, and a P1 or P2 face mask (P2 masks are sometimes referred to as N95 masks) to minimise exposure to dust. Do not bury CCA treated timber ash.

6

Not all treated & toxic timber these days looks like that.

7

Indoor framing wood is usually non-pressure treated pine, but maybe the interior wall the OP mentions was put up by a former homeowner who didn’t know any better and used pressure treated lumber? Just a guess.

A friend of mine owns a house built in 1928, and when he did some renovation on a kitchen floor it required ripping out some of the sub floor, which was made of 70+ year old oak. I joined him for several fires in his backyard burning that well seasoned oak. That stuff burned and smelled great.

8

Any framing that touches concrete needs to be pressure treated per current building codes. Primarily applies to bottom plates of stud walls resting directly on the foundation or on a slab. Other than that it would be highly unlikely for pressure treated to be used in a stud wall since it has a tendency to warp as it dries out over time.

9

How old was the wall? The wood might have been treated with creosote, which also isn’t healthy to burn.

10

The ends are spray painted; you might be getting burning spray paint smell.

11

Chromated copper arsenate-treated wood was phased out about 20 years ago. The newer chemical formulation used in pressure -treated wood is copper-based but doesn’t contain arsenic. Not sure how it would smell if burned.

Note that some dyed mulches are made from construction debris and might contain/leach undesirable contaminants.

12

This is the answer. When cooking or smoking food you use hardwood, Construction wood comes out of evergreen forests, you don’t want to cook with that.