EWS TMD, N Gauge, Modern Era

[m8internet]

Its the Peco track that has warped not the base board

Hence, why I asked what method you have used to apply the track to the baseboard
If the baseboard has not warped then there is another issue, as N gauge track does not normally warp
It will expand and contract, the fishplates and IRJs normally take up this movement

Finally, what about the temperature in the loft; variable or consistent?

One thing I learned during my first construction was to get consistent temperature, and I now have a thermometer in the room to ensure the room is kept to between 18'C and 22'C

[Tractor Matt]

Hence, why I asked what method you have used to apply the track to the baseboard
If the baseboard has not warped then there is another issue, as N gauge track does not normally warp
It will expand and contract, the fishplates and IRJs normally take up this movement

Finally, what about the temperature in the loft; variable or consistent?

One thing I learned during my first construction was to get consistent temperature, and I now have a thermometer in the room to ensure the room is kept to between 18'C and 22'C

This track has been pinned at 6 cm intervals and warped inbetween each pin. The track was laid in summer, so i didn't want to leave any big expansion gaps due to the winter temperatures, and scared that gaps would appear when the temperature drops. The temperature is consistent within the seasons but can drop to just below freezing in the winter and upto 40 / 50 degrees in the mid summer.

[m8internet]

This track has been pinned at 6 cm intervals and warped inbetween each pin

I too have pinned the track
What method have you used to connect each piece of track?
Are the sections of rail hard against each other or are there gaps?